Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3881 insertions, 0 deletions

diff --git a/layout/base/RestyleManager.cpp b/layout/base/RestyleManager.cpp
new file mode 100644
index 0000000000..9c313a254c
--- /dev/null
+++ b/layout/base/RestyleManager.cpp
@@ -0,0 +1,3881 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/RestyleManager.h"
+
+#include "mozilla/AnimationUtils.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/ComputedStyle.h"
+#include "mozilla/ComputedStyleInlines.h"
+#include "mozilla/DocumentStyleRootIterator.h"
+#include "mozilla/EffectSet.h"
+#include "mozilla/GeckoBindings.h"
+#include "mozilla/LayerAnimationInfo.h"
+#include "mozilla/layers/AnimationInfo.h"
+#include "mozilla/layout/ScrollAnchorContainer.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/PresShellInlines.h"
+#include "mozilla/ProfilerLabels.h"
+#include "mozilla/ServoBindings.h"
+#include "mozilla/ServoStyleSetInlines.h"
+#include "mozilla/StaticPrefs_layout.h"
+#include "mozilla/SVGIntegrationUtils.h"
+#include "mozilla/SVGObserverUtils.h"
+#include "mozilla/SVGTextFrame.h"
+#include "mozilla/SVGUtils.h"
+#include "mozilla/Unused.h"
+#include "mozilla/ViewportFrame.h"
+#include "mozilla/IntegerRange.h"
+#include "mozilla/dom/ChildIterator.h"
+#include "mozilla/dom/DocumentInlines.h"
+#include "mozilla/dom/ElementInlines.h"
+#include "mozilla/dom/HTMLBodyElement.h"
+#include "mozilla/dom/HTMLInputElement.h"
+
+#include "ScrollSnap.h"
+#include "nsAnimationManager.h"
+#include "nsBlockFrame.h"
+#include "nsIScrollableFrame.h"
+#include "nsContentUtils.h"
+#include "nsCSSFrameConstructor.h"
+#include "nsCSSRendering.h"
+#include "nsDocShell.h"
+#include "nsIFrame.h"
+#include "nsIFrameInlines.h"
+#include "nsImageFrame.h"
+#include "nsPlaceholderFrame.h"
+#include "nsPrintfCString.h"
+#include "nsRefreshDriver.h"
+#include "nsStyleChangeList.h"
+#include "nsStyleUtil.h"
+#include "nsTransitionManager.h"
+#include "StickyScrollContainer.h"
+#include "ActiveLayerTracker.h"
+
+#ifdef ACCESSIBILITY
+#  include "nsAccessibilityService.h"
+#endif
+
+using mozilla::layers::AnimationInfo;
+using mozilla::layout::ScrollAnchorContainer;
+
+using namespace mozilla::dom;
+using namespace mozilla::layers;
+
+namespace mozilla {
+
+RestyleManager::RestyleManager(nsPresContext* aPresContext)
+    : mPresContext(aPresContext),
+      mRestyleGeneration(1),
+      mUndisplayedRestyleGeneration(1),
+      mInStyleRefresh(false),
+      mAnimationGeneration(0) {
+  MOZ_ASSERT(mPresContext);
+}
+
+void RestyleManager::ContentInserted(nsIContent* aChild) {
+  MOZ_ASSERT(aChild->GetParentNode());
+  if (aChild->IsElement()) {
+    StyleSet()->MaybeInvalidateForElementInsertion(*aChild->AsElement());
+  }
+  RestyleForInsertOrChange(aChild);
+}
+
+void RestyleManager::ContentAppended(nsIContent* aFirstNewContent) {
+  auto* container = aFirstNewContent->GetParentNode();
+  MOZ_ASSERT(container);
+
+#ifdef DEBUG
+  {
+    for (nsIContent* cur = aFirstNewContent; cur; cur = cur->GetNextSibling()) {
+      NS_ASSERTION(!cur->IsRootOfNativeAnonymousSubtree(),
+                   "anonymous nodes should not be in child lists");
+    }
+  }
+#endif
+  StyleSet()->MaybeInvalidateForElementAppend(*aFirstNewContent);
+
+  const auto selectorFlags = container->GetSelectorFlags() &
+                             NodeSelectorFlags::AllSimpleRestyleFlagsForAppend;
+  if (!selectorFlags) {
+    return;
+  }
+
+  // The container cannot be a document.
+  MOZ_ASSERT(container->IsElement() || container->IsShadowRoot());
+
+  if (selectorFlags & NodeSelectorFlags::HasEmptySelector) {
+    // see whether we need to restyle the container
+    bool wasEmpty = true;  // :empty or :-moz-only-whitespace
+    for (nsIContent* cur = container->GetFirstChild(); cur != aFirstNewContent;
+         cur = cur->GetNextSibling()) {
+      // We don't know whether we're testing :empty or :-moz-only-whitespace,
+      // so be conservative and assume :-moz-only-whitespace (i.e., make
+      // IsSignificantChild less likely to be true, and thus make us more
+      // likely to restyle).
+      if (nsStyleUtil::IsSignificantChild(cur, false)) {
+        wasEmpty = false;
+        break;
+      }
+    }
+    if (wasEmpty && container->IsElement()) {
+      RestyleForEmptyChange(container->AsElement());
+      return;
+    }
+  }
+
+  if (selectorFlags & NodeSelectorFlags::HasSlowSelector) {
+    if (container->IsElement()) {
+      auto* containerElement = container->AsElement();
+      PostRestyleEvent(containerElement, RestyleHint::RestyleSubtree(),
+                       nsChangeHint(0));
+      if (selectorFlags & NodeSelectorFlags::HasSlowSelectorNthAll) {
+        StyleSet()->MaybeInvalidateRelativeSelectorForNthDependencyFromSibling(
+            containerElement->GetFirstElementChild());
+      }
+    } else {
+      RestylePreviousSiblings(aFirstNewContent);
+      RestyleSiblingsStartingWith(aFirstNewContent);
+    }
+    // Restyling the container is the most we can do here, so we're done.
+    return;
+  }
+
+  if (selectorFlags & NodeSelectorFlags::HasEdgeChildSelector) {
+    // restyle the last element child before this node
+    for (nsIContent* cur = aFirstNewContent->GetPreviousSibling(); cur;
+         cur = cur->GetPreviousSibling()) {
+      if (cur->IsElement()) {
+        auto* element = cur->AsElement();
+        PostRestyleEvent(element, RestyleHint::RestyleSubtree(),
+                         nsChangeHint(0));
+        StyleSet()->MaybeInvalidateRelativeSelectorForNthEdgeDependency(
+            *element);
+        break;
+      }
+    }
+  }
+}
+
+void RestyleManager::RestylePreviousSiblings(nsIContent* aStartingSibling) {
+  for (nsIContent* sibling = aStartingSibling; sibling;
+       sibling = sibling->GetPreviousSibling()) {
+    if (auto* element = Element::FromNode(sibling)) {
+      PostRestyleEvent(element, RestyleHint::RestyleSubtree(), nsChangeHint(0));
+    }
+  }
+}
+
+void RestyleManager::RestyleSiblingsStartingWith(nsIContent* aStartingSibling) {
+  for (nsIContent* sibling = aStartingSibling; sibling;
+       sibling = sibling->GetNextSibling()) {
+    if (auto* element = Element::FromNode(sibling)) {
+      PostRestyleEvent(element, RestyleHint::RestyleSubtree(), nsChangeHint(0));
+    }
+  }
+}
+
+void RestyleManager::RestyleForEmptyChange(Element* aContainer) {
+  PostRestyleEvent(aContainer, RestyleHint::RestyleSubtree(), nsChangeHint(0));
+  StyleSet()->MaybeInvalidateRelativeSelectorForEmptyDependency(*aContainer);
+
+  // In some cases (:empty + E, :empty ~ E), a change in the content of
+  // an element requires restyling its parent's siblings.
+  nsIContent* grandparent = aContainer->GetParent();
+  if (!grandparent || !(grandparent->GetSelectorFlags() &
+                        NodeSelectorFlags::HasSlowSelectorLaterSiblings)) {
+    return;
+  }
+  RestyleSiblingsStartingWith(aContainer->GetNextSibling());
+}
+
+void RestyleManager::MaybeRestyleForEdgeChildChange(nsINode* aContainer,
+                                                    nsIContent* aChangedChild) {
+  MOZ_ASSERT(aContainer->GetSelectorFlags() &
+             NodeSelectorFlags::HasEdgeChildSelector);
+  MOZ_ASSERT(aChangedChild->GetParent() == aContainer);
+  // restyle the previously-first element child if it is after this node
+  bool passedChild = false;
+  for (nsIContent* content = aContainer->GetFirstChild(); content;
+       content = content->GetNextSibling()) {
+    if (content == aChangedChild) {
+      passedChild = true;
+      continue;
+    }
+    if (content->IsElement()) {
+      if (passedChild) {
+        auto* element = content->AsElement();
+        PostRestyleEvent(element, RestyleHint::RestyleSubtree(),
+                         nsChangeHint(0));
+        StyleSet()->MaybeInvalidateRelativeSelectorForNthEdgeDependency(
+            *element);
+      }
+      break;
+    }
+  }
+  // restyle the previously-last element child if it is before this node
+  passedChild = false;
+  for (nsIContent* content = aContainer->GetLastChild(); content;
+       content = content->GetPreviousSibling()) {
+    if (content == aChangedChild) {
+      passedChild = true;
+      continue;
+    }
+    if (content->IsElement()) {
+      if (passedChild) {
+        auto* element = content->AsElement();
+        PostRestyleEvent(element, RestyleHint::RestyleSubtree(),
+                         nsChangeHint(0));
+        StyleSet()->MaybeInvalidateRelativeSelectorForNthEdgeDependency(
+            *element);
+      }
+      break;
+    }
+  }
+}
+
+template <typename CharT>
+bool WhitespaceOnly(const CharT* aBuffer, size_t aUpTo) {
+  for (auto index : IntegerRange(aUpTo)) {
+    if (!dom::IsSpaceCharacter(aBuffer[index])) {
+      return false;
+    }
+  }
+  return true;
+}
+
+template <typename CharT>
+bool WhitespaceOnlyChangedOnAppend(const CharT* aBuffer, size_t aOldLength,
+                                   size_t aNewLength) {
+  MOZ_ASSERT(aOldLength <= aNewLength);
+  if (!WhitespaceOnly(aBuffer, aOldLength)) {
+    // The old text was already not whitespace-only.
+    return false;
+  }
+
+  return !WhitespaceOnly(aBuffer + aOldLength, aNewLength - aOldLength);
+}
+
+static bool HasAnySignificantSibling(Element* aContainer, nsIContent* aChild) {
+  MOZ_ASSERT(aChild->GetParent() == aContainer);
+  for (nsIContent* child = aContainer->GetFirstChild(); child;
+       child = child->GetNextSibling()) {
+    if (child == aChild) {
+      continue;
+    }
+    // We don't know whether we're testing :empty or :-moz-only-whitespace,
+    // so be conservative and assume :-moz-only-whitespace (i.e., make
+    // IsSignificantChild less likely to be true, and thus make us more
+    // likely to restyle).
+    if (nsStyleUtil::IsSignificantChild(child, false)) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+void RestyleManager::CharacterDataChanged(
+    nsIContent* aContent, const CharacterDataChangeInfo& aInfo) {
+  nsINode* parent = aContent->GetParentNode();
+  MOZ_ASSERT(parent, "How were we notified of a stray node?");
+
+  const auto slowSelectorFlags =
+      parent->GetSelectorFlags() & NodeSelectorFlags::AllSimpleRestyleFlags;
+  if (!(slowSelectorFlags & (NodeSelectorFlags::HasEmptySelector |
+                             NodeSelectorFlags::HasEdgeChildSelector))) {
+    // Nothing to do, no other slow selector can change as a result of this.
+    return;
+  }
+
+  if (!aContent->IsText()) {
+    // Doesn't matter to styling (could be a processing instruction or a
+    // comment), it can't change whether any selectors match or don't.
+    return;
+  }
+
+  if (MOZ_UNLIKELY(!parent->IsElement())) {
+    MOZ_ASSERT(parent->IsShadowRoot());
+    return;
+  }
+
+  if (MOZ_UNLIKELY(aContent->IsRootOfNativeAnonymousSubtree())) {
+    // This is an anonymous node and thus isn't in child lists, so isn't taken
+    // into account for selector matching the relevant selectors here.
+    return;
+  }
+
+  // Handle appends specially since they're common and we can know both the old
+  // and the new text exactly.
+  //
+  // TODO(emilio): This could be made much more general if :-moz-only-whitespace
+  // / :-moz-first-node and :-moz-last-node didn't exist. In that case we only
+  // need to know whether we went from empty to non-empty, and that's trivial to
+  // know, with CharacterDataChangeInfo...
+  if (!aInfo.mAppend) {
+    // FIXME(emilio): This restyles unnecessarily if the text node is the only
+    // child of the parent element. Fortunately, it's uncommon to have such
+    // nodes and this not being an append.
+    //
+    // See the testcase in bug 1427625 for a test-case that triggers this.
+    RestyleForInsertOrChange(aContent);
+    return;
+  }
+
+  const nsTextFragment* text = &aContent->AsText()->TextFragment();
+
+  const size_t oldLength = aInfo.mChangeStart;
+  const size_t newLength = text->GetLength();
+
+  const bool emptyChanged = !oldLength && newLength;
+
+  const bool whitespaceOnlyChanged =
+      text->Is2b()
+          ? WhitespaceOnlyChangedOnAppend(text->Get2b(), oldLength, newLength)
+          : WhitespaceOnlyChangedOnAppend(text->Get1b(), oldLength, newLength);
+
+  if (!emptyChanged && !whitespaceOnlyChanged) {
+    return;
+  }
+
+  if (slowSelectorFlags & NodeSelectorFlags::HasEmptySelector) {
+    if (!HasAnySignificantSibling(parent->AsElement(), aContent)) {
+      // We used to be empty, restyle the parent.
+      RestyleForEmptyChange(parent->AsElement());
+      return;
+    }
+  }
+
+  if (slowSelectorFlags & NodeSelectorFlags::HasEdgeChildSelector) {
+    MaybeRestyleForEdgeChildChange(parent, aContent);
+  }
+}
+
+// Restyling for a ContentInserted or CharacterDataChanged notification.
+// This could be used for ContentRemoved as well if we got the
+// notification before the removal happened (and sometimes
+// CharacterDataChanged is more like a removal than an addition).
+// The comments are written and variables are named in terms of it being
+// a ContentInserted notification.
+void RestyleManager::RestyleForInsertOrChange(nsIContent* aChild) {
+  nsINode* container = aChild->GetParentNode();
+  MOZ_ASSERT(container);
+
+  const auto selectorFlags =
+      container->GetSelectorFlags() & NodeSelectorFlags::AllSimpleRestyleFlags;
+  if (!selectorFlags) {
+    return;
+  }
+
+  NS_ASSERTION(!aChild->IsRootOfNativeAnonymousSubtree(),
+               "anonymous nodes should not be in child lists");
+
+  // The container cannot be a document.
+  MOZ_ASSERT(container->IsElement() || container->IsShadowRoot());
+
+  if (selectorFlags & NodeSelectorFlags::HasEmptySelector &&
+      container->IsElement()) {
+    // See whether we need to restyle the container due to :empty /
+    // :-moz-only-whitespace.
+    const bool wasEmpty =
+        !HasAnySignificantSibling(container->AsElement(), aChild);
+    if (wasEmpty) {
+      // FIXME(emilio): When coming from CharacterDataChanged this can restyle
+      // unnecessarily. Also can restyle unnecessarily if aChild is not
+      // significant anyway, though that's more unlikely.
+      RestyleForEmptyChange(container->AsElement());
+      return;
+    }
+  }
+
+  if (selectorFlags & NodeSelectorFlags::HasSlowSelector) {
+    if (container->IsElement()) {
+      auto* containerElement = container->AsElement();
+      PostRestyleEvent(containerElement, RestyleHint::RestyleSubtree(),
+                       nsChangeHint(0));
+      if (selectorFlags & NodeSelectorFlags::HasSlowSelectorNthAll) {
+        StyleSet()->MaybeInvalidateRelativeSelectorForNthDependencyFromSibling(
+            containerElement->GetFirstElementChild());
+      }
+    } else {
+      RestylePreviousSiblings(aChild);
+      RestyleSiblingsStartingWith(aChild);
+    }
+    // Restyling the container is the most we can do here, so we're done.
+    return;
+  }
+
+  if (selectorFlags & NodeSelectorFlags::HasSlowSelectorLaterSiblings) {
+    // Restyle all later siblings.
+    RestyleSiblingsStartingWith(aChild->GetNextSibling());
+    if (selectorFlags & NodeSelectorFlags::HasSlowSelectorNthAll) {
+      StyleSet()->MaybeInvalidateRelativeSelectorForNthDependencyFromSibling(
+          aChild->GetNextElementSibling());
+    }
+  }
+
+  if (selectorFlags & NodeSelectorFlags::HasEdgeChildSelector) {
+    MaybeRestyleForEdgeChildChange(container, aChild);
+  }
+}
+
+void RestyleManager::ContentRemoved(nsIContent* aOldChild,
+                                    nsIContent* aFollowingSibling) {
+  auto* container = aOldChild->GetParentNode();
+  MOZ_ASSERT(container);
+
+  // Computed style data isn't useful for detached nodes, and we'll need to
+  // recompute it anyway if we ever insert the nodes back into a document.
+  if (auto* element = Element::FromNode(aOldChild)) {
+    RestyleManager::ClearServoDataFromSubtree(element);
+    // If this element is undisplayed or may have undisplayed descendants, we
+    // need to invalidate the cache, since there's the unlikely event of those
+    // elements getting destroyed and their addresses reused in a way that we
+    // look up the cache with their address for a different element before it's
+    // invalidated.
+    IncrementUndisplayedRestyleGeneration();
+  }
+  if (aOldChild->IsElement()) {
+    StyleSet()->MaybeInvalidateForElementRemove(*aOldChild->AsElement(),
+                                                aFollowingSibling);
+  }
+
+  const auto selectorFlags =
+      container->GetSelectorFlags() & NodeSelectorFlags::AllSimpleRestyleFlags;
+  if (!selectorFlags) {
+    return;
+  }
+
+  if (aOldChild->IsRootOfNativeAnonymousSubtree()) {
+    // This should be an assert, but this is called incorrectly in
+    // HTMLEditor::DeleteRefToAnonymousNode and the assertions were clogging
+    // up the logs.  Make it an assert again when that's fixed.
+    MOZ_ASSERT(aOldChild->GetProperty(nsGkAtoms::restylableAnonymousNode),
+               "anonymous nodes should not be in child lists (bug 439258)");
+  }
+
+  // The container cannot be a document.
+  MOZ_ASSERT(container->IsElement() || container->IsShadowRoot());
+
+  if (selectorFlags & NodeSelectorFlags::HasEmptySelector &&
+      container->IsElement()) {
+    // see whether we need to restyle the container
+    bool isEmpty = true;  // :empty or :-moz-only-whitespace
+    for (nsIContent* child = container->GetFirstChild(); child;
+         child = child->GetNextSibling()) {
+      // We don't know whether we're testing :empty or :-moz-only-whitespace,
+      // so be conservative and assume :-moz-only-whitespace (i.e., make
+      // IsSignificantChild less likely to be true, and thus make us more
+      // likely to restyle).
+      if (nsStyleUtil::IsSignificantChild(child, false)) {
+        isEmpty = false;
+        break;
+      }
+    }
+    if (isEmpty && container->IsElement()) {
+      RestyleForEmptyChange(container->AsElement());
+      return;
+    }
+  }
+
+  if (selectorFlags & NodeSelectorFlags::HasSlowSelector) {
+    if (container->IsElement()) {
+      auto* containerElement = container->AsElement();
+      PostRestyleEvent(containerElement, RestyleHint::RestyleSubtree(),
+                       nsChangeHint(0));
+      if (selectorFlags & NodeSelectorFlags::HasSlowSelectorNthAll) {
+        StyleSet()->MaybeInvalidateRelativeSelectorForNthDependencyFromSibling(
+            containerElement->GetFirstElementChild());
+      }
+    } else {
+      RestylePreviousSiblings(aOldChild);
+      RestyleSiblingsStartingWith(aOldChild);
+    }
+    // Restyling the container is the most we can do here, so we're done.
+    return;
+  }
+
+  if (selectorFlags & NodeSelectorFlags::HasSlowSelectorLaterSiblings) {
+    // Restyle all later siblings.
+    RestyleSiblingsStartingWith(aFollowingSibling);
+    if (selectorFlags & NodeSelectorFlags::HasSlowSelectorNthAll) {
+      Element* nextSibling =
+          aFollowingSibling ? aFollowingSibling->IsElement()
+                                  ? aFollowingSibling->AsElement()
+                                  : aFollowingSibling->GetNextElementSibling()
+                            : nullptr;
+      StyleSet()->MaybeInvalidateRelativeSelectorForNthDependencyFromSibling(
+          nextSibling);
+    }
+  }
+
+  if (selectorFlags & NodeSelectorFlags::HasEdgeChildSelector) {
+    // restyle the now-first element child if it was after aOldChild
+    bool reachedFollowingSibling = false;
+    for (nsIContent* content = container->GetFirstChild(); content;
+         content = content->GetNextSibling()) {
+      if (content == aFollowingSibling) {
+        reachedFollowingSibling = true;
+        // do NOT continue here; we might want to restyle this node
+      }
+      if (content->IsElement()) {
+        if (reachedFollowingSibling) {
+          auto* element = content->AsElement();
+          PostRestyleEvent(element, RestyleHint::RestyleSubtree(),
+                           nsChangeHint(0));
+          StyleSet()->MaybeInvalidateRelativeSelectorForNthEdgeDependency(
+              *element);
+        }
+        break;
+      }
+    }
+    // restyle the now-last element child if it was before aOldChild
+    reachedFollowingSibling = (aFollowingSibling == nullptr);
+    for (nsIContent* content = container->GetLastChild(); content;
+         content = content->GetPreviousSibling()) {
+      if (content->IsElement()) {
+        if (reachedFollowingSibling) {
+          auto* element = content->AsElement();
+          PostRestyleEvent(element, RestyleHint::RestyleSubtree(),
+                           nsChangeHint(0));
+          StyleSet()->MaybeInvalidateRelativeSelectorForNthEdgeDependency(
+              *element);
+        }
+        break;
+      }
+      if (content == aFollowingSibling) {
+        reachedFollowingSibling = true;
+      }
+    }
+  }
+}
+
+static bool StateChangeMayAffectFrame(const Element& aElement,
+                                      const nsIFrame& aFrame,
+                                      ElementState aStates) {
+  const bool brokenChanged = aStates.HasState(ElementState::BROKEN);
+  if (!brokenChanged) {
+    return false;
+  }
+
+  if (aFrame.IsGeneratedContentFrame()) {
+    // If it's other generated content, ignore state changes on it.
+    return aElement.IsHTMLElement(nsGkAtoms::mozgeneratedcontentimage);
+  }
+
+  if (aElement.IsAnyOfHTMLElements(nsGkAtoms::object, nsGkAtoms::embed)) {
+    // Broken affects object fallback behavior.
+    return true;
+  }
+
+  const bool mightChange = [&] {
+    if (aElement.IsHTMLElement(nsGkAtoms::img)) {
+      return true;
+    }
+    const auto* input = HTMLInputElement::FromNode(aElement);
+    return input && input->ControlType() == FormControlType::InputImage;
+  }();
+
+  if (!mightChange) {
+    return false;
+  }
+
+  const bool needsImageFrame =
+      nsImageFrame::ImageFrameTypeFor(aElement, *aFrame.Style()) !=
+      nsImageFrame::ImageFrameType::None;
+  return needsImageFrame != aFrame.IsImageFrameOrSubclass();
+}
+
+static bool RepaintForAppearance(nsIFrame& aFrame, const Element& aElement,
+                                 ElementState aStateMask) {
+  if (aStateMask.HasAtLeastOneOfStates(ElementState::HOVER |
+                                       ElementState::ACTIVE) &&
+      aElement.IsAnyOfXULElements(nsGkAtoms::checkbox, nsGkAtoms::radio)) {
+    // The checkbox inside these elements inherit hover state and so on, see
+    // nsNativeTheme::GetContentState.
+    // FIXME(emilio): Would be nice to not have these hard-coded.
+    return true;
+  }
+  auto appearance = aFrame.StyleDisplay()->EffectiveAppearance();
+  if (appearance == StyleAppearance::None) {
+    return false;
+  }
+  nsPresContext* pc = aFrame.PresContext();
+  nsITheme* theme = pc->Theme();
+  if (!theme->ThemeSupportsWidget(pc, &aFrame, appearance)) {
+    return false;
+  }
+  bool repaint = false;
+  theme->WidgetStateChanged(&aFrame, appearance, nullptr, &repaint, nullptr);
+  return repaint;
+}
+
+/**
+ * Calculates the change hint and the restyle hint for a given content state
+ * change.
+ */
+static nsChangeHint ChangeForContentStateChange(const Element& aElement,
+                                                ElementState aStateMask) {
+  auto changeHint = nsChangeHint(0);
+
+  // Any change to a content state that affects which frames we construct
+  // must lead to a frame reconstruct here if we already have a frame.
+  // Note that we never decide through non-CSS means to not create frames
+  // based on content states, so if we already don't have a frame we don't
+  // need to force a reframe -- if it's needed, the HasStateDependentStyle
+  // call will handle things.
+  if (nsIFrame* primaryFrame = aElement.GetPrimaryFrame()) {
+    if (StateChangeMayAffectFrame(aElement, *primaryFrame, aStateMask)) {
+      return nsChangeHint_ReconstructFrame;
+    }
+    if (RepaintForAppearance(*primaryFrame, aElement, aStateMask)) {
+      changeHint |= nsChangeHint_RepaintFrame;
+    }
+    primaryFrame->ElementStateChanged(aStateMask);
+  }
+
+  if (aStateMask.HasState(ElementState::VISITED)) {
+    // Exposing information to the page about whether the link is
+    // visited or not isn't really something we can worry about here.
+    // FIXME: We could probably do this a bit better.
+    changeHint |= nsChangeHint_RepaintFrame;
+  }
+
+  // This changes the applicable text-transform in the editor root.
+  if (aStateMask.HasState(ElementState::REVEALED)) {
+    // This is the same change hint as tweaking text-transform.
+    changeHint |= NS_STYLE_HINT_REFLOW;
+  }
+
+  return changeHint;
+}
+
+#ifdef DEBUG
+/* static */
+nsCString RestyleManager::ChangeHintToString(nsChangeHint aHint) {
+  nsCString result;
+  bool any = false;
+  const char* names[] = {"RepaintFrame",
+                         "NeedReflow",
+                         "ClearAncestorIntrinsics",
+                         "ClearDescendantIntrinsics",
+                         "NeedDirtyReflow",
+                         "UpdateCursor",
+                         "UpdateEffects",
+                         "UpdateOpacityLayer",
+                         "UpdateTransformLayer",
+                         "ReconstructFrame",
+                         "UpdateOverflow",
+                         "UpdateSubtreeOverflow",
+                         "UpdatePostTransformOverflow",
+                         "UpdateParentOverflow",
+                         "ChildrenOnlyTransform",
+                         "RecomputePosition",
+                         "UpdateContainingBlock",
+                         "BorderStyleNoneChange",
+                         "SchedulePaint",
+                         "NeutralChange",
+                         "InvalidateRenderingObservers",
+                         "ReflowChangesSizeOrPosition",
+                         "UpdateComputedBSize",
+                         "UpdateUsesOpacity",
+                         "UpdateBackgroundPosition",
+                         "AddOrRemoveTransform",
+                         "ScrollbarChange",
+                         "UpdateTableCellSpans",
+                         "VisibilityChange"};
+  static_assert(nsChangeHint_AllHints ==
+                    static_cast<uint32_t>((1ull << ArrayLength(names)) - 1),
+                "Name list doesn't match change hints.");
+  uint32_t hint =
+      aHint & static_cast<uint32_t>((1ull << ArrayLength(names)) - 1);
+  uint32_t rest =
+      aHint & ~static_cast<uint32_t>((1ull << ArrayLength(names)) - 1);
+  if ((hint & NS_STYLE_HINT_REFLOW) == NS_STYLE_HINT_REFLOW) {
+    result.AppendLiteral("NS_STYLE_HINT_REFLOW");
+    hint = hint & ~NS_STYLE_HINT_REFLOW;
+    any = true;
+  } else if ((hint & nsChangeHint_AllReflowHints) ==
+             nsChangeHint_AllReflowHints) {
+    result.AppendLiteral("nsChangeHint_AllReflowHints");
+    hint = hint & ~nsChangeHint_AllReflowHints;
+    any = true;
+  } else if ((hint & NS_STYLE_HINT_VISUAL) == NS_STYLE_HINT_VISUAL) {
+    result.AppendLiteral("NS_STYLE_HINT_VISUAL");
+    hint = hint & ~NS_STYLE_HINT_VISUAL;
+    any = true;
+  }
+  for (uint32_t i = 0; i < ArrayLength(names); i++) {
+    if (hint & (1u << i)) {
+      if (any) {
+        result.AppendLiteral(" | ");
+      }
+      result.AppendPrintf("nsChangeHint_%s", names[i]);
+      any = true;
+    }
+  }
+  if (rest) {
+    if (any) {
+      result.AppendLiteral(" | ");
+    }
+    result.AppendPrintf("0x%0x", rest);
+  } else {
+    if (!any) {
+      result.AppendLiteral("nsChangeHint(0)");
+    }
+  }
+  return result;
+}
+#endif
+
+/**
+ * Frame construction helpers follow.
+ */
+#ifdef DEBUG
+static bool gInApplyRenderingChangeToTree = false;
+#endif
+
+/**
+ * Sync views on the frame and all of it's descendants (following placeholders).
+ * The change hint should be some combination of nsChangeHint_RepaintFrame,
+ * nsChangeHint_UpdateOpacityLayer and nsChangeHint_SchedulePaint, nothing else.
+ */
+static void SyncViewsAndInvalidateDescendants(nsIFrame*, nsChangeHint);
+
+static void StyleChangeReflow(nsIFrame* aFrame, nsChangeHint aHint);
+
+/**
+ * This helper function is used to find the correct SVG frame to target when we
+ * encounter nsChangeHint_ChildrenOnlyTransform; needed since sometimes we end
+ * up handling that hint while processing hints for one of the SVG frame's
+ * ancestor frames.
+ *
+ * The reason that we sometimes end up trying to process the hint for an
+ * ancestor of the SVG frame that the hint is intended for is due to the way we
+ * process restyle events. ApplyRenderingChangeToTree adjusts the frame from
+ * the restyled element's principle frame to one of its ancestor frames based
+ * on what nsCSSRendering::FindBackground returns, since the background style
+ * may have been propagated up to an ancestor frame. Processing hints using an
+ * ancestor frame is fine in general, but nsChangeHint_ChildrenOnlyTransform is
+ * a special case since it is intended to update a specific frame.
+ */
+static nsIFrame* GetFrameForChildrenOnlyTransformHint(nsIFrame* aFrame) {
+  if (aFrame->IsViewportFrame()) {
+    // This happens if the root-<svg> is fixed positioned, in which case we
+    // can't use aFrame->GetContent() to find the primary frame, since
+    // GetContent() returns nullptr for ViewportFrame.
+    aFrame = aFrame->PrincipalChildList().FirstChild();
+  }
+  // For an nsHTMLScrollFrame, this will get the SVG frame that has the
+  // children-only transforms:
+  aFrame = aFrame->GetContent()->GetPrimaryFrame();
+  if (aFrame->IsSVGOuterSVGFrame()) {
+    aFrame = aFrame->PrincipalChildList().FirstChild();
+    MOZ_ASSERT(aFrame->IsSVGOuterSVGAnonChildFrame(),
+               "Where is the SVGOuterSVGFrame's anon child??");
+  }
+  MOZ_ASSERT(aFrame->IsSVGContainerFrame(),
+             "Children-only transforms only expected on SVG frames");
+  return aFrame;
+}
+
+// This function tries to optimize a position style change by either
+// moving aFrame or ignoring the style change when it's safe to do so.
+// It returns true when that succeeds, otherwise it posts a reflow request
+// and returns false.
+static bool RecomputePosition(nsIFrame* aFrame) {
+  // It's pointless to move around frames that have never been reflowed or
+  // are dirty (i.e. they will be reflowed), or aren't affected by position
+  // styles.
+  if (aFrame->HasAnyStateBits(NS_FRAME_FIRST_REFLOW | NS_FRAME_IS_DIRTY |
+                              NS_FRAME_SVG_LAYOUT)) {
+    return true;
+  }
+
+  // Don't process position changes on table frames, since we already handle
+  // the dynamic position change on the table wrapper frame, and the
+  // reflow-based fallback code path also ignores positions on inner table
+  // frames.
+  if (aFrame->IsTableFrame()) {
+    return true;
+  }
+
+  const nsStyleDisplay* display = aFrame->StyleDisplay();
+  // Changes to the offsets of a non-positioned element can safely be ignored.
+  if (display->mPosition == StylePositionProperty::Static) {
+    return true;
+  }
+
+  // Don't process position changes on frames which have views or the ones which
+  // have a view somewhere in their descendants, because the corresponding view
+  // needs to be repositioned properly as well.
+  if (aFrame->HasView() ||
+      aFrame->HasAnyStateBits(NS_FRAME_HAS_CHILD_WITH_VIEW)) {
+    return false;
+  }
+
+  if (aFrame->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW)) {
+    // If the frame has an intrinsic block-size, we resolve its 'auto' margins
+    // after doing layout, since we need to know the frame's block size. See
+    // nsAbsoluteContainingBlock::ResolveAutoMarginsAfterLayout().
+    //
+    // Since the size of the frame doesn't change, we could modify the below
+    // computation to compute the margin correctly without doing a full reflow,
+    // however we decided to try doing a full reflow for now.
+    if (aFrame->HasIntrinsicKeywordForBSize()) {
+      WritingMode wm = aFrame->GetWritingMode();
+      const auto* styleMargin = aFrame->StyleMargin();
+      if (styleMargin->HasBlockAxisAuto(wm)) {
+        return false;
+      }
+    }
+    // Flexbox and Grid layout supports CSS Align and the optimizations below
+    // don't support that yet.
+    nsIFrame* ph = aFrame->GetPlaceholderFrame();
+    if (ph && ph->HasAnyStateBits(PLACEHOLDER_STATICPOS_NEEDS_CSSALIGN)) {
+      return false;
+    }
+  }
+
+  // If we need to reposition any descendant that depends on our static
+  // position, then we also can't take the optimized path.
+  //
+  // TODO(emilio): It may be worth trying to find them and try to call
+  // RecomputePosition on them too instead of disabling the optimization...
+  if (aFrame->DescendantMayDependOnItsStaticPosition()) {
+    return false;
+  }
+
+  aFrame->SchedulePaint();
+
+  auto postPendingScrollAnchorOrResnap = [](nsIFrame* frame) {
+    if (frame->IsInScrollAnchorChain()) {
+      ScrollAnchorContainer* container = ScrollAnchorContainer::FindFor(frame);
+      frame->PresShell()->PostPendingScrollAnchorAdjustment(container);
+    }
+
+    // We need to trigger re-snapping to this content if we snapped to the
+    // content on the last scroll operation.
+    ScrollSnapUtils::PostPendingResnapIfNeededFor(frame);
+  };
+
+  // For relative positioning, we can simply update the frame rect
+  if (display->IsRelativelyOrStickyPositionedStyle()) {
+    if (aFrame->IsGridItem()) {
+      // A grid item's CB is its grid area, not the parent frame content area
+      // as is assumed below.
+      return false;
+    }
+    // Move the frame
+    if (display->mPosition == StylePositionProperty::Sticky) {
+      // Update sticky positioning for an entire element at once, starting with
+      // the first continuation or ib-split sibling.
+      // It's rare that the frame we already have isn't already the first
+      // continuation or ib-split sibling, but it can happen when styles differ
+      // across continuations such as ::first-line or ::first-letter, and in
+      // those cases we will generally (but maybe not always) do the work twice.
+      nsIFrame* firstContinuation =
+          nsLayoutUtils::FirstContinuationOrIBSplitSibling(aFrame);
+
+      StickyScrollContainer::ComputeStickyOffsets(firstContinuation);
+      StickyScrollContainer* ssc =
+          StickyScrollContainer::GetStickyScrollContainerForFrame(
+              firstContinuation);
+      if (ssc) {
+        ssc->PositionContinuations(firstContinuation);
+      }
+    } else {
+      MOZ_ASSERT(display->IsRelativelyPositionedStyle(),
+                 "Unexpected type of positioning");
+      for (nsIFrame* cont = aFrame; cont;
+           cont = nsLayoutUtils::GetNextContinuationOrIBSplitSibling(cont)) {
+        nsIFrame* cb = cont->GetContainingBlock();
+        WritingMode wm = cb->GetWritingMode();
+        const LogicalSize cbSize = cb->ContentSize();
+        const LogicalMargin newLogicalOffsets =
+            ReflowInput::ComputeRelativeOffsets(wm, cont, cbSize);
+        const nsMargin newOffsets = newLogicalOffsets.GetPhysicalMargin(wm);
+
+        // ReflowInput::ApplyRelativePositioning would work here, but
+        // since we've already checked mPosition and aren't changing the frame's
+        // normal position, go ahead and add the offsets directly.
+        // First, we need to ensure that the normal position is stored though.
+        bool hasProperty;
+        nsPoint normalPosition = cont->GetNormalPosition(&hasProperty);
+        if (!hasProperty) {
+          cont->AddProperty(nsIFrame::NormalPositionProperty(), normalPosition);
+        }
+        cont->SetPosition(normalPosition +
+                          nsPoint(newOffsets.left, newOffsets.top));
+      }
+    }
+
+    postPendingScrollAnchorOrResnap(aFrame);
+    return true;
+  }
+
+  // For the absolute positioning case, set up a fake HTML reflow input for
+  // the frame, and then get the offsets and size from it. If the frame's size
+  // doesn't need to change, we can simply update the frame position. Otherwise
+  // we fall back to a reflow.
+  UniquePtr<gfxContext> rc =
+      aFrame->PresShell()->CreateReferenceRenderingContext();
+
+  // Construct a bogus parent reflow input so that there's a usable reflow input
+  // for the containing block.
+  nsIFrame* parentFrame = aFrame->GetParent();
+  WritingMode parentWM = parentFrame->GetWritingMode();
+  WritingMode frameWM = aFrame->GetWritingMode();
+  LogicalSize parentSize = parentFrame->GetLogicalSize();
+
+  nsFrameState savedState = parentFrame->GetStateBits();
+  ReflowInput parentReflowInput(aFrame->PresContext(), parentFrame, rc.get(),
+                                parentSize);
+  parentFrame->RemoveStateBits(~nsFrameState(0));
+  parentFrame->AddStateBits(savedState);
+
+  // The bogus parent state here was created with no parent state of its own,
+  // and therefore it won't have an mCBReflowInput set up.
+  // But we may need one (for InitCBReflowInput in a child state), so let's
+  // try to create one here for the cases where it will be needed.
+  Maybe<ReflowInput> cbReflowInput;
+  nsIFrame* cbFrame = parentFrame->GetContainingBlock();
+  if (cbFrame && (aFrame->GetContainingBlock() != parentFrame ||
+                  parentFrame->IsTableFrame())) {
+    const auto cbWM = cbFrame->GetWritingMode();
+    LogicalSize cbSize = cbFrame->GetLogicalSize();
+    cbReflowInput.emplace(cbFrame->PresContext(), cbFrame, rc.get(), cbSize);
+    cbReflowInput->SetComputedLogicalMargin(
+        cbWM, cbFrame->GetLogicalUsedMargin(cbWM));
+    cbReflowInput->SetComputedLogicalPadding(
+        cbWM, cbFrame->GetLogicalUsedPadding(cbWM));
+    cbReflowInput->SetComputedLogicalBorderPadding(
+        cbWM, cbFrame->GetLogicalUsedBorderAndPadding(cbWM));
+    parentReflowInput.mCBReflowInput = cbReflowInput.ptr();
+  }
+
+  NS_WARNING_ASSERTION(parentSize.ISize(parentWM) != NS_UNCONSTRAINEDSIZE &&
+                           parentSize.BSize(parentWM) != NS_UNCONSTRAINEDSIZE,
+                       "parentSize should be valid");
+  parentReflowInput.SetComputedISize(std::max(parentSize.ISize(parentWM), 0));
+  parentReflowInput.SetComputedBSize(std::max(parentSize.BSize(parentWM), 0));
+  parentReflowInput.SetComputedLogicalMargin(parentWM, LogicalMargin(parentWM));
+
+  parentReflowInput.SetComputedLogicalPadding(
+      parentWM, parentFrame->GetLogicalUsedPadding(parentWM));
+  parentReflowInput.SetComputedLogicalBorderPadding(
+      parentWM, parentFrame->GetLogicalUsedBorderAndPadding(parentWM));
+  LogicalSize availSize = parentSize.ConvertTo(frameWM, parentWM);
+  availSize.BSize(frameWM) = NS_UNCONSTRAINEDSIZE;
+
+  ViewportFrame* viewport = do_QueryFrame(parentFrame);
+  nsSize cbSize =
+      viewport
+          ? viewport->AdjustReflowInputAsContainingBlock(&parentReflowInput)
+                .Size()
+          : aFrame->GetContainingBlock()->GetSize();
+  const nsMargin& parentBorder =
+      parentReflowInput.mStyleBorder->GetComputedBorder();
+  cbSize -= nsSize(parentBorder.LeftRight(), parentBorder.TopBottom());
+  LogicalSize lcbSize(frameWM, cbSize);
+  ReflowInput reflowInput(aFrame->PresContext(), parentReflowInput, aFrame,
+                          availSize, Some(lcbSize));
+  nscoord computedISize = reflowInput.ComputedISize();
+  nscoord computedBSize = reflowInput.ComputedBSize();
+  const auto frameBP = reflowInput.ComputedLogicalBorderPadding(frameWM);
+  computedISize += frameBP.IStartEnd(frameWM);
+  if (computedBSize != NS_UNCONSTRAINEDSIZE) {
+    computedBSize += frameBP.BStartEnd(frameWM);
+  }
+  LogicalSize logicalSize = aFrame->GetLogicalSize(frameWM);
+  nsSize size = aFrame->GetSize();
+  // The RecomputePosition hint is not used if any offset changed between auto
+  // and non-auto. If computedSize.height == NS_UNCONSTRAINEDSIZE then the new
+  // element height will be its intrinsic height, and since 'top' and 'bottom''s
+  // auto-ness hasn't changed, the old height must also be its intrinsic
+  // height, which we can assume hasn't changed (or reflow would have
+  // been triggered).
+  if (computedISize == logicalSize.ISize(frameWM) &&
+      (computedBSize == NS_UNCONSTRAINEDSIZE ||
+       computedBSize == logicalSize.BSize(frameWM))) {
+    // If we're solving for 'left' or 'top', then compute it here, in order to
+    // match the reflow code path.
+    //
+    // TODO(emilio): It'd be nice if this did logical math instead, but it seems
+    // to me the math should work out on vertical writing modes as well. See Bug
+    // 1675861 for some hints.
+    const nsMargin offset = reflowInput.ComputedPhysicalOffsets();
+    const nsMargin margin = reflowInput.ComputedPhysicalMargin();
+
+    nscoord left = offset.left;
+    if (left == NS_AUTOOFFSET) {
+      left =
+          cbSize.width - offset.right - margin.right - size.width - margin.left;
+    }
+
+    nscoord top = offset.top;
+    if (top == NS_AUTOOFFSET) {
+      top = cbSize.height - offset.bottom - margin.bottom - size.height -
+            margin.top;
+    }
+
+    // Move the frame
+    nsPoint pos(parentBorder.left + left + margin.left,
+                parentBorder.top + top + margin.top);
+    aFrame->SetPosition(pos);
+
+    postPendingScrollAnchorOrResnap(aFrame);
+    return true;
+  }
+
+  // Fall back to a reflow
+  return false;
+}
+
+/**
+ * Return true if aFrame's subtree has placeholders for out-of-flow content
+ * that would be affected due to the change to
+ * `aPossiblyChangingContainingBlock` (and thus would need to get reframed).
+ *
+ * In particular, this function returns true if there are placeholders whose OOF
+ * frames may need to be reparented (via reframing) as a result of whatever
+ * change actually happened.
+ *
+ * The `aIs{Abs,Fixed}PosContainingBlock` params represent whether
+ * `aPossiblyChangingContainingBlock` is a containing block for abs pos / fixed
+ * pos stuff, respectively, for the _new_ style that the frame already has, not
+ * the old one.
+ */
+static bool ContainingBlockChangeAffectsDescendants(
+    nsIFrame* aPossiblyChangingContainingBlock, nsIFrame* aFrame,
+    bool aIsAbsPosContainingBlock, bool aIsFixedPosContainingBlock) {
+  // All fixed-pos containing blocks should also be abs-pos containing blocks.
+  MOZ_ASSERT_IF(aIsFixedPosContainingBlock, aIsAbsPosContainingBlock);
+
+  for (const auto& childList : aFrame->ChildLists()) {
+    for (nsIFrame* f : childList.mList) {
+      if (f->IsPlaceholderFrame()) {
+        nsIFrame* outOfFlow = nsPlaceholderFrame::GetRealFrameForPlaceholder(f);
+        // If SVG text frames could appear here, they could confuse us since
+        // they ignore their position style ... but they can't.
+        NS_ASSERTION(!outOfFlow->IsInSVGTextSubtree(),
+                     "SVG text frames can't be out of flow");
+        // Top-layer frames don't change containing block based on direct
+        // ancestors.
+        auto* display = outOfFlow->StyleDisplay();
+        if (display->IsAbsolutelyPositionedStyle() &&
+            display->mTopLayer == StyleTopLayer::None) {
+          const bool isContainingBlock =
+              aIsFixedPosContainingBlock ||
+              (aIsAbsPosContainingBlock &&
+               display->mPosition == StylePositionProperty::Absolute);
+          // NOTE(emilio): aPossiblyChangingContainingBlock is guaranteed to be
+          // a first continuation, see the assertion in the caller.
+          nsIFrame* parent = outOfFlow->GetParent()->FirstContinuation();
+          if (isContainingBlock) {
+            // If we are becoming a containing block, we only need to reframe if
+            // this oof's current containing block is an ancestor of the new
+            // frame.
+            if (parent != aPossiblyChangingContainingBlock &&
+                nsLayoutUtils::IsProperAncestorFrame(
+                    parent, aPossiblyChangingContainingBlock)) {
+              return true;
+            }
+          } else {
+            // If we are not a containing block anymore, we only need to reframe
+            // if we are the current containing block of the oof frame.
+            if (parent == aPossiblyChangingContainingBlock) {
+              return true;
+            }
+          }
+        }
+      }
+      // NOTE:  It's tempting to check f->IsAbsPosContainingBlock() or
+      // f->IsFixedPosContainingBlock() here.  However, that would only
+      // be testing the *new* style of the frame, which might exclude
+      // descendants that currently have this frame as an abs-pos
+      // containing block.  Taking the codepath where we don't reframe
+      // could lead to an unsafe call to
+      // cont->MarkAsNotAbsoluteContainingBlock() before we've reframed
+      // the descendant and taken it off the absolute list.
+      if (ContainingBlockChangeAffectsDescendants(
+              aPossiblyChangingContainingBlock, f, aIsAbsPosContainingBlock,
+              aIsFixedPosContainingBlock)) {
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
+// Returns the frame that would serve as the containing block for aFrame's
+// positioned descendants, if aFrame had styles to make it a CB for such
+// descendants. (Typically this is just aFrame itself, or its insertion frame).
+//
+// Returns nullptr if this frame can't be easily determined.
+static nsIFrame* ContainingBlockForFrame(nsIFrame* aFrame) {
+  if (aFrame->IsFieldSetFrame()) {
+    // FIXME: This should be easily implementable.
+    return nullptr;
+  }
+  nsIFrame* insertionFrame = aFrame->GetContentInsertionFrame();
+  if (insertionFrame == aFrame) {
+    return insertionFrame;
+  }
+  // Generally frames with a different insertion frame are hard to deal with,
+  // but scrollframes are easy because the containing block is just the
+  // insertion frame.
+  if (aFrame->IsScrollFrame()) {
+    return insertionFrame;
+  }
+  // Combobox frames are easy as well because they can't have positioned
+  // children anyways.
+  // Button and table cell frames are also easy because the containing block is
+  // the frame itself.
+  if (aFrame->IsComboboxControlFrame() || aFrame->IsHTMLButtonControlFrame() ||
+      aFrame->IsTableCellFrame()) {
+    return aFrame;
+  }
+  return nullptr;
+}
+
+static bool NeedToReframeToUpdateContainingBlock(nsIFrame* aFrame,
+                                                 nsIFrame* aMaybeChangingCB) {
+  // NOTE: This looks at the new style.
+  const bool isFixedContainingBlock = aFrame->IsFixedPosContainingBlock();
+  MOZ_ASSERT_IF(isFixedContainingBlock, aFrame->IsAbsPosContainingBlock());
+
+  const bool isAbsPosContainingBlock =
+      isFixedContainingBlock || aFrame->IsAbsPosContainingBlock();
+
+  for (nsIFrame* f = aFrame; f;
+       f = nsLayoutUtils::GetNextContinuationOrIBSplitSibling(f)) {
+    if (ContainingBlockChangeAffectsDescendants(aMaybeChangingCB, f,
+                                                isAbsPosContainingBlock,
+                                                isFixedContainingBlock)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+static void DoApplyRenderingChangeToTree(nsIFrame* aFrame,
+                                         nsChangeHint aChange) {
+  MOZ_ASSERT(gInApplyRenderingChangeToTree,
+             "should only be called within ApplyRenderingChangeToTree");
+
+  for (; aFrame;
+       aFrame = nsLayoutUtils::GetNextContinuationOrIBSplitSibling(aFrame)) {
+    // Invalidate and sync views on all descendant frames, following
+    // placeholders. We don't need to update transforms in
+    // SyncViewsAndInvalidateDescendants, because there can't be any
+    // out-of-flows or popups that need to be transformed; all out-of-flow
+    // descendants of the transformed element must also be descendants of the
+    // transformed frame.
+    SyncViewsAndInvalidateDescendants(
+        aFrame, nsChangeHint(aChange & (nsChangeHint_RepaintFrame |
+                                        nsChangeHint_UpdateOpacityLayer |
+                                        nsChangeHint_SchedulePaint)));
+    // This must be set to true if the rendering change needs to
+    // invalidate content.  If it's false, a composite-only paint
+    // (empty transaction) will be scheduled.
+    bool needInvalidatingPaint = false;
+
+    // if frame has view, will already be invalidated
+    if (aChange & nsChangeHint_RepaintFrame) {
+      // Note that this whole block will be skipped when painting is suppressed
+      // (due to our caller ApplyRendingChangeToTree() discarding the
+      // nsChangeHint_RepaintFrame hint).  If you add handling for any other
+      // hints within this block, be sure that they too should be ignored when
+      // painting is suppressed.
+      needInvalidatingPaint = true;
+      aFrame->InvalidateFrameSubtree();
+      if ((aChange & nsChangeHint_UpdateEffects) &&
+          aFrame->HasAnyStateBits(NS_FRAME_SVG_LAYOUT)) {
+        // Need to update our overflow rects:
+        SVGUtils::ScheduleReflowSVG(aFrame);
+      }
+
+      ActiveLayerTracker::NotifyNeedsRepaint(aFrame);
+    }
+    if (aChange & nsChangeHint_UpdateOpacityLayer) {
+      // FIXME/bug 796697: we can get away with empty transactions for
+      // opacity updates in many cases.
+      needInvalidatingPaint = true;
+
+      ActiveLayerTracker::NotifyRestyle(aFrame, eCSSProperty_opacity);
+      if (SVGIntegrationUtils::UsingEffectsForFrame(aFrame)) {
+        // SVG effects paints the opacity without using
+        // nsDisplayOpacity. We need to invalidate manually.
+        aFrame->InvalidateFrameSubtree();
+      }
+    }
+    if ((aChange & nsChangeHint_UpdateTransformLayer) &&
+        aFrame->IsTransformed()) {
+      // Note: All the transform-like properties should map to the same
+      // layer activity index, so does the restyle count. Therefore, using
+      // eCSSProperty_transform should be fine.
+      ActiveLayerTracker::NotifyRestyle(aFrame, eCSSProperty_transform);
+      needInvalidatingPaint = true;
+    }
+    if (aChange & nsChangeHint_ChildrenOnlyTransform) {
+      needInvalidatingPaint = true;
+      nsIFrame* childFrame = GetFrameForChildrenOnlyTransformHint(aFrame)
+                                 ->PrincipalChildList()
+                                 .FirstChild();
+      for (; childFrame; childFrame = childFrame->GetNextSibling()) {
+        // Note: All the transform-like properties should map to the same
+        // layer activity index, so does the restyle count. Therefore, using
+        // eCSSProperty_transform should be fine.
+        ActiveLayerTracker::NotifyRestyle(childFrame, eCSSProperty_transform);
+      }
+    }
+    if (aChange & nsChangeHint_SchedulePaint) {
+      needInvalidatingPaint = true;
+    }
+    aFrame->SchedulePaint(needInvalidatingPaint
+                              ? nsIFrame::PAINT_DEFAULT
+                              : nsIFrame::PAINT_COMPOSITE_ONLY);
+  }
+}
+
+static void SyncViewsAndInvalidateDescendants(nsIFrame* aFrame,
+                                              nsChangeHint aChange) {
+  MOZ_ASSERT(gInApplyRenderingChangeToTree,
+             "should only be called within ApplyRenderingChangeToTree");
+
+  NS_ASSERTION(nsChangeHint_size_t(aChange) ==
+                   (aChange & (nsChangeHint_RepaintFrame |
+                               nsChangeHint_UpdateOpacityLayer |
+                               nsChangeHint_SchedulePaint)),
+               "Invalid change flag");
+
+  aFrame->SyncFrameViewProperties();
+
+  for (const auto& [list, listID] : aFrame->ChildLists()) {
+    for (nsIFrame* child : list) {
+      if (!child->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW)) {
+        // only do frames that don't have placeholders
+        if (child->IsPlaceholderFrame()) {
+          // do the out-of-flow frame and its continuations
+          nsIFrame* outOfFlowFrame =
+              nsPlaceholderFrame::GetRealFrameForPlaceholder(child);
+          DoApplyRenderingChangeToTree(outOfFlowFrame, aChange);
+        } else if (listID == FrameChildListID::Popup) {
+          DoApplyRenderingChangeToTree(child, aChange);
+        } else {  // regular frame
+          SyncViewsAndInvalidateDescendants(child, aChange);
+        }
+      }
+    }
+  }
+}
+
+static void ApplyRenderingChangeToTree(PresShell* aPresShell, nsIFrame* aFrame,
+                                       nsChangeHint aChange) {
+  // We check StyleDisplay()->HasTransformStyle() in addition to checking
+  // IsTransformed() since we can get here for some frames that don't support
+  // CSS transforms, and table frames, which are their own odd-ball, since the
+  // transform is handled by their wrapper, which _also_ gets a separate hint.
+  NS_ASSERTION(!(aChange & nsChangeHint_UpdateTransformLayer) ||
+                   aFrame->IsTransformed() ||
+                   aFrame->StyleDisplay()->HasTransformStyle(),
+               "Unexpected UpdateTransformLayer hint");
+
+  if (aPresShell->IsPaintingSuppressed()) {
+    // Don't allow synchronous rendering changes when painting is turned off.
+    aChange &= ~nsChangeHint_RepaintFrame;
+    if (!aChange) {
+      return;
+    }
+  }
+
+// Trigger rendering updates by damaging this frame and any
+// continuations of this frame.
+#ifdef DEBUG
+  gInApplyRenderingChangeToTree = true;
+#endif
+  if (aChange & nsChangeHint_RepaintFrame) {
+    // If the frame is the primary frame of either the body element or
+    // the html element, we propagate the repaint change hint to the
+    // viewport. This is necessary for background and scrollbar colors
+    // propagation.
+    if (aFrame->IsPrimaryFrameOfRootOrBodyElement()) {
+      nsIFrame* rootFrame = aPresShell->GetRootFrame();
+      MOZ_ASSERT(rootFrame, "No root frame?");
+      DoApplyRenderingChangeToTree(rootFrame, nsChangeHint_RepaintFrame);
+      aChange &= ~nsChangeHint_RepaintFrame;
+      if (!aChange) {
+        return;
+      }
+    }
+  }
+  DoApplyRenderingChangeToTree(aFrame, aChange);
+#ifdef DEBUG
+  gInApplyRenderingChangeToTree = false;
+#endif
+}
+
+static void AddSubtreeToOverflowTracker(
+    nsIFrame* aFrame, OverflowChangedTracker& aOverflowChangedTracker) {
+  if (aFrame->FrameMaintainsOverflow()) {
+    aOverflowChangedTracker.AddFrame(aFrame,
+                                     OverflowChangedTracker::CHILDREN_CHANGED);
+  }
+  for (const auto& childList : aFrame->ChildLists()) {
+    for (nsIFrame* child : childList.mList) {
+      AddSubtreeToOverflowTracker(child, aOverflowChangedTracker);
+    }
+  }
+}
+
+static void StyleChangeReflow(nsIFrame* aFrame, nsChangeHint aHint) {
+  IntrinsicDirty dirtyType;
+  if (aHint & nsChangeHint_ClearDescendantIntrinsics) {
+    NS_ASSERTION(aHint & nsChangeHint_ClearAncestorIntrinsics,
+                 "Please read the comments in nsChangeHint.h");
+    NS_ASSERTION(aHint & nsChangeHint_NeedDirtyReflow,
+                 "ClearDescendantIntrinsics requires NeedDirtyReflow");
+    dirtyType = IntrinsicDirty::FrameAncestorsAndDescendants;
+  } else if ((aHint & nsChangeHint_UpdateComputedBSize) &&
+             aFrame->HasAnyStateBits(
+                 NS_FRAME_DESCENDANT_INTRINSIC_ISIZE_DEPENDS_ON_BSIZE)) {
+    dirtyType = IntrinsicDirty::FrameAncestorsAndDescendants;
+  } else if (aHint & nsChangeHint_ClearAncestorIntrinsics) {
+    dirtyType = IntrinsicDirty::FrameAndAncestors;
+  } else {
+    dirtyType = IntrinsicDirty::None;
+  }
+
+  if (aHint & nsChangeHint_UpdateComputedBSize) {
+    aFrame->SetHasBSizeChange(true);
+  }
+
+  nsFrameState dirtyBits;
+  if (aFrame->HasAnyStateBits(NS_FRAME_FIRST_REFLOW)) {
+    dirtyBits = nsFrameState(0);
+  } else if ((aHint & nsChangeHint_NeedDirtyReflow) ||
+             dirtyType == IntrinsicDirty::FrameAncestorsAndDescendants) {
+    dirtyBits = NS_FRAME_IS_DIRTY;
+  } else {
+    dirtyBits = NS_FRAME_HAS_DIRTY_CHILDREN;
+  }
+
+  // If we're not going to clear any intrinsic sizes on the frames, and
+  // there are no dirty bits to set, then there's nothing to do.
+  if (dirtyType == IntrinsicDirty::None && !dirtyBits) return;
+
+  ReflowRootHandling rootHandling;
+  if (aHint & nsChangeHint_ReflowChangesSizeOrPosition) {
+    rootHandling = ReflowRootHandling::PositionOrSizeChange;
+  } else {
+    rootHandling = ReflowRootHandling::NoPositionOrSizeChange;
+  }
+
+  do {
+    aFrame->PresShell()->FrameNeedsReflow(aFrame, dirtyType, dirtyBits,
+                                          rootHandling);
+    aFrame = nsLayoutUtils::GetNextContinuationOrIBSplitSibling(aFrame);
+  } while (aFrame);
+}
+
+// Get the next sibling which might have a frame.  This only considers siblings
+// that stylo post-traversal looks at, so only elements and text.  In
+// particular, it ignores comments.
+static nsIContent* NextSiblingWhichMayHaveFrame(nsIContent* aContent) {
+  for (nsIContent* next = aContent->GetNextSibling(); next;
+       next = next->GetNextSibling()) {
+    if (next->IsElement() || next->IsText()) {
+      return next;
+    }
+  }
+
+  return nullptr;
+}
+
+// If |aFrame| is dirty or has dirty children, then we can skip updating
+// overflows since that will happen when it's reflowed.
+static inline bool CanSkipOverflowUpdates(const nsIFrame* aFrame) {
+  return aFrame->HasAnyStateBits(NS_FRAME_IS_DIRTY |
+                                 NS_FRAME_HAS_DIRTY_CHILDREN);
+}
+
+static inline void TryToDealWithScrollbarChange(nsChangeHint& aHint,
+                                                nsIContent* aContent,
+                                                nsIFrame* aFrame,
+                                                nsPresContext* aPc) {
+  if (!(aHint & nsChangeHint_ScrollbarChange)) {
+    return;
+  }
+  aHint &= ~nsChangeHint_ScrollbarChange;
+  if (aHint & nsChangeHint_ReconstructFrame) {
+    return;
+  }
+
+  MOZ_ASSERT(aFrame, "If we're not reframing, we ought to have a frame");
+
+  const bool isRoot = aContent->IsInUncomposedDoc() && !aContent->GetParent();
+
+  // Only bother with this if we're the root or the body element, since:
+  //  (a) It'd be *expensive* to reframe these particular nodes.  They're
+  //      at the root, so reframing would mean rebuilding the world.
+  //  (b) It's often *unnecessary* to reframe for "overflow" changes on
+  //      these particular nodes.  In general, the only reason we reframe
+  //      for "overflow" changes is so we can construct (or destroy) a
+  //      scrollframe & scrollbars -- and the html/body nodes often don't
+  //      need their own scrollframe/scrollbars because they coopt the ones
+  //      on the viewport (which always exist). So depending on whether
+  //      that's happening, we can skip the reframe for these nodes.
+  if (isRoot || aContent->IsHTMLElement(nsGkAtoms::body)) {
+    // If the restyled element provided/provides the scrollbar styles for
+    // the viewport before and/or after this restyle, AND it's not coopting
+    // that responsibility from some other element (which would need
+    // reconstruction to make its own scrollframe now), THEN: we don't need
+    // to reconstruct - we can just reflow, because no scrollframe is being
+    // added/removed.
+    Element* prevOverride = aPc->GetViewportScrollStylesOverrideElement();
+    Element* newOverride = aPc->UpdateViewportScrollStylesOverride();
+
+    const auto ProvidesScrollbarStyles = [&](nsIContent* aOverride) {
+      if (aOverride) {
+        return aOverride == aContent;
+      }
+      return isRoot;
+    };
+
+    if (ProvidesScrollbarStyles(prevOverride) ||
+        ProvidesScrollbarStyles(newOverride)) {
+      // If we get here, the restyled element provided the scrollbar styles
+      // for viewport before this restyle, OR it will provide them after.
+      if (!prevOverride || !newOverride || prevOverride == newOverride) {
+        // If we get here, the restyled element is NOT replacing (or being
+        // replaced by) some other element as the viewport's
+        // scrollbar-styles provider. (If it were, we'd potentially need to
+        // reframe to create a dedicated scrollframe for whichever element
+        // is being booted from providing viewport scrollbar styles.)
+        //
+        // Under these conditions, we're OK to assume that this "overflow"
+        // change only impacts the root viewport's scrollframe, which
+        // already exists, so we can simply reflow instead of reframing.
+        if (nsIScrollableFrame* sf = do_QueryFrame(aFrame)) {
+          sf->MarkScrollbarsDirtyForReflow();
+        } else if (nsIScrollableFrame* sf =
+                       aPc->PresShell()->GetRootScrollFrameAsScrollable()) {
+          sf->MarkScrollbarsDirtyForReflow();
+        }
+        aHint |= nsChangeHint_ReflowHintsForScrollbarChange;
+      } else {
+        // If we changed the override element, we need to reconstruct as the old
+        // override element might start / stop being scrollable.
+        aHint |= nsChangeHint_ReconstructFrame;
+      }
+      return;
+    }
+  }
+
+  const bool scrollable = aFrame->StyleDisplay()->IsScrollableOverflow();
+  if (nsIScrollableFrame* sf = do_QueryFrame(aFrame)) {
+    if (scrollable && sf->HasAllNeededScrollbars()) {
+      sf->MarkScrollbarsDirtyForReflow();
+      // Once we've created scrollbars for a frame, don't bother reconstructing
+      // it just to remove them if we still need a scroll frame.
+      aHint |= nsChangeHint_ReflowHintsForScrollbarChange;
+      return;
+    }
+  } else if (aFrame->IsTextInputFrame()) {
+    // input / textarea for the most part don't honor overflow themselves, the
+    // editor root will deal with the change if needed.
+    // However the textarea intrinsic size relies on GetDesiredScrollbarSizes(),
+    // so we need to reflow the textarea itself, not just the inner control.
+    aHint |= nsChangeHint_ReflowHintsForScrollbarChange;
+    return;
+  } else if (!scrollable) {
+    // Something changed, but we don't have nor will have a scroll frame,
+    // there's nothing to do here.
+    return;
+  }
+
+  // Oh well, we couldn't optimize it out, just reconstruct frames for the
+  // subtree.
+  aHint |= nsChangeHint_ReconstructFrame;
+}
+
+static void TryToHandleContainingBlockChange(nsChangeHint& aHint,
+                                             nsIFrame* aFrame) {
+  if (!(aHint & nsChangeHint_UpdateContainingBlock)) {
+    return;
+  }
+  if (aHint & nsChangeHint_ReconstructFrame) {
+    return;
+  }
+  MOZ_ASSERT(aFrame, "If we're not reframing, we ought to have a frame");
+  nsIFrame* containingBlock = ContainingBlockForFrame(aFrame);
+  if (!containingBlock ||
+      NeedToReframeToUpdateContainingBlock(aFrame, containingBlock)) {
+    // The frame has positioned children that need to be reparented, or it can't
+    // easily be converted to/from being an abs-pos container correctly.
+    aHint |= nsChangeHint_ReconstructFrame;
+    return;
+  }
+  const bool isCb = aFrame->IsAbsPosContainingBlock();
+
+  // The absolute container should be containingBlock.
+  for (nsIFrame* cont = containingBlock; cont;
+       cont = nsLayoutUtils::GetNextContinuationOrIBSplitSibling(cont)) {
+    // Normally frame construction would set state bits as needed,
+    // but we're not going to reconstruct the frame so we need to set
+    // them. It's because we need to set this state on each affected frame
+    // that we can't coalesce nsChangeHint_UpdateContainingBlock hints up
+    // to ancestors (i.e. it can't be an change hint that is handled for
+    // descendants).
+    if (isCb) {
+      if (!cont->IsAbsoluteContainer() &&
+          cont->HasAnyStateBits(NS_FRAME_CAN_HAVE_ABSPOS_CHILDREN)) {
+        cont->MarkAsAbsoluteContainingBlock();
+      }
+    } else if (cont->IsAbsoluteContainer()) {
+      if (cont->HasAbsolutelyPositionedChildren()) {
+        // If |cont| still has absolutely positioned children,
+        // we can't call MarkAsNotAbsoluteContainingBlock.  This
+        // will remove a frame list that still has children in
+        // it that we need to keep track of.
+        // The optimization of removing it isn't particularly
+        // important, although it does mean we skip some tests.
+        NS_WARNING("skipping removal of absolute containing block");
+      } else {
+        cont->MarkAsNotAbsoluteContainingBlock();
+      }
+    }
+  }
+}
+
+void RestyleManager::ProcessRestyledFrames(nsStyleChangeList& aChangeList) {
+  NS_ASSERTION(!nsContentUtils::IsSafeToRunScript(),
+               "Someone forgot a script blocker");
+
+  // See bug 1378219 comment 9:
+  // Recursive calls here are a bit worrying, but apparently do happen in the
+  // wild (although not currently in any of our automated tests). Try to get a
+  // stack from Nightly/Dev channel to figure out what's going on and whether
+  // it's OK.
+  MOZ_DIAGNOSTIC_ASSERT(!mDestroyedFrames, "ProcessRestyledFrames recursion");
+
+  if (aChangeList.IsEmpty()) {
+    return;
+  }
+
+  // If mDestroyedFrames is null, we want to create a new hashtable here
+  // and destroy it on exit; but if it is already non-null (because we're in
+  // a recursive call), we will continue to use the existing table to
+  // accumulate destroyed frames, and NOT clear mDestroyedFrames on exit.
+  // We use a MaybeClearDestroyedFrames helper to conditionally reset the
+  // mDestroyedFrames pointer when this method returns.
+  typedef decltype(mDestroyedFrames) DestroyedFramesT;
+  class MOZ_RAII MaybeClearDestroyedFrames {
+   private:
+    DestroyedFramesT& mDestroyedFramesRef;  // ref to caller's mDestroyedFrames
+    const bool mResetOnDestruction;
+
+   public:
+    explicit MaybeClearDestroyedFrames(DestroyedFramesT& aTarget)
+        : mDestroyedFramesRef(aTarget),
+          mResetOnDestruction(!aTarget)  // reset only if target starts out null
+    {}
+    ~MaybeClearDestroyedFrames() {
+      if (mResetOnDestruction) {
+        mDestroyedFramesRef.reset(nullptr);
+      }
+    }
+  };
+
+  MaybeClearDestroyedFrames maybeClear(mDestroyedFrames);
+  if (!mDestroyedFrames) {
+    mDestroyedFrames = MakeUnique<nsTHashSet<const nsIFrame*>>();
+  }
+
+  AUTO_PROFILER_LABEL("RestyleManager::ProcessRestyledFrames", LAYOUT);
+
+  nsPresContext* presContext = PresContext();
+  nsCSSFrameConstructor* frameConstructor = presContext->FrameConstructor();
+
+  bool didUpdateCursor = false;
+
+  for (size_t i = 0; i < aChangeList.Length(); ++i) {
+    // Collect and coalesce adjacent siblings for lazy frame construction.
+    // Eventually it would be even better to make RecreateFramesForContent
+    // accept a range and coalesce all adjacent reconstructs (bug 1344139).
+    size_t lazyRangeStart = i;
+    while (i < aChangeList.Length() && aChangeList[i].mContent &&
+           aChangeList[i].mContent->HasFlag(NODE_NEEDS_FRAME) &&
+           (i == lazyRangeStart ||
+            NextSiblingWhichMayHaveFrame(aChangeList[i - 1].mContent) ==
+                aChangeList[i].mContent)) {
+      MOZ_ASSERT(aChangeList[i].mHint & nsChangeHint_ReconstructFrame);
+      MOZ_ASSERT(!aChangeList[i].mFrame);
+      ++i;
+    }
+    if (i != lazyRangeStart) {
+      nsIContent* start = aChangeList[lazyRangeStart].mContent;
+      nsIContent* end =
+          NextSiblingWhichMayHaveFrame(aChangeList[i - 1].mContent);
+      if (!end) {
+        frameConstructor->ContentAppended(
+            start, nsCSSFrameConstructor::InsertionKind::Sync);
+      } else {
+        frameConstructor->ContentRangeInserted(
+            start, end, nsCSSFrameConstructor::InsertionKind::Sync);
+      }
+    }
+    for (size_t j = lazyRangeStart; j < i; ++j) {
+      MOZ_ASSERT(!aChangeList[j].mContent->GetPrimaryFrame() ||
+                 !aChangeList[j].mContent->HasFlag(NODE_NEEDS_FRAME));
+    }
+    if (i == aChangeList.Length()) {
+      break;
+    }
+
+    const nsStyleChangeData& data = aChangeList[i];
+    nsIFrame* frame = data.mFrame;
+    nsIContent* content = data.mContent;
+    nsChangeHint hint = data.mHint;
+    bool didReflowThisFrame = false;
+
+    NS_ASSERTION(!(hint & nsChangeHint_AllReflowHints) ||
+                     (hint & nsChangeHint_NeedReflow),
+                 "Reflow hint bits set without actually asking for a reflow");
+
+    // skip any frame that has been destroyed due to a ripple effect
+    if (frame && mDestroyedFrames->Contains(frame)) {
+      continue;
+    }
+
+    if (frame && frame->GetContent() != content) {
+      // XXXbz this is due to image maps messing with the primary frame of
+      // <area>s.  See bug 135040.  Remove this block once that's fixed.
+      frame = nullptr;
+      if (!(hint & nsChangeHint_ReconstructFrame)) {
+        continue;
+      }
+    }
+
+    TryToDealWithScrollbarChange(hint, content, frame, presContext);
+    TryToHandleContainingBlockChange(hint, frame);
+
+    if (hint & nsChangeHint_ReconstructFrame) {
+      // If we ever start passing true here, be careful of restyles
+      // that involve a reframe and animations.  In particular, if the
+      // restyle we're processing here is an animation restyle, but
+      // the style resolution we will do for the frame construction
+      // happens async when we're not in an animation restyle already,
+      // problems could arise.
+      // We could also have problems with triggering of CSS transitions
+      // on elements whose frames are reconstructed, since we depend on
+      // the reconstruction happening synchronously.
+      frameConstructor->RecreateFramesForContent(
+          content, nsCSSFrameConstructor::InsertionKind::Sync);
+      continue;
+    }
+
+    MOZ_ASSERT(frame, "This shouldn't happen");
+    if (hint & nsChangeHint_AddOrRemoveTransform) {
+      for (nsIFrame* cont = frame; cont;
+           cont = nsLayoutUtils::GetNextContinuationOrIBSplitSibling(cont)) {
+        if (cont->StyleDisplay()->HasTransform(cont)) {
+          cont->AddStateBits(NS_FRAME_MAY_BE_TRANSFORMED);
+        }
+        // Don't remove NS_FRAME_MAY_BE_TRANSFORMED since it may still be
+        // transformed by other means. It's OK to have the bit even if it's
+        // not needed.
+      }
+      // When dropping a running transform animation we will first add an
+      // nsChangeHint_UpdateTransformLayer hint as part of the animation-only
+      // restyle. During the subsequent regular restyle, if the animation was
+      // the only reason the element had any transform applied, we will add
+      // nsChangeHint_AddOrRemoveTransform as part of the regular restyle.
+      //
+      // With the Gecko backend, these two change hints are processed
+      // after each restyle but when using the Servo backend they accumulate
+      // and are processed together after we have already removed the
+      // transform as part of the regular restyle. Since we don't actually
+      // need the nsChangeHint_UpdateTransformLayer hint if we already have
+      // a nsChangeHint_AddOrRemoveTransform hint, and since we
+      // will fail an assertion in ApplyRenderingChangeToTree if we try
+      // specify nsChangeHint_UpdateTransformLayer but don't have any
+      // transform style, we just drop the unneeded hint here.
+      hint &= ~nsChangeHint_UpdateTransformLayer;
+    }
+
+    if (!frame->FrameMaintainsOverflow()) {
+      // frame does not maintain overflow rects, so avoid calling
+      // FinishAndStoreOverflow on it:
+      hint &=
+          ~(nsChangeHint_UpdateOverflow | nsChangeHint_ChildrenOnlyTransform |
+            nsChangeHint_UpdatePostTransformOverflow |
+            nsChangeHint_UpdateParentOverflow |
+            nsChangeHint_UpdateSubtreeOverflow);
+    }
+
+    if (!frame->HasAnyStateBits(NS_FRAME_MAY_BE_TRANSFORMED)) {
+      // Frame can not be transformed, and thus a change in transform will
+      // have no effect and we should not use either
+      // nsChangeHint_UpdatePostTransformOverflow or
+      // nsChangeHint_UpdateTransformLayerhint.
+      hint &= ~(nsChangeHint_UpdatePostTransformOverflow |
+                nsChangeHint_UpdateTransformLayer);
+    }
+
+    if ((hint & nsChangeHint_UpdateEffects) &&
+        frame == nsLayoutUtils::FirstContinuationOrIBSplitSibling(frame)) {
+      SVGObserverUtils::UpdateEffects(frame);
+    }
+    if ((hint & nsChangeHint_InvalidateRenderingObservers) ||
+        ((hint & nsChangeHint_UpdateOpacityLayer) &&
+         frame->HasAnyStateBits(NS_FRAME_SVG_LAYOUT))) {
+      SVGObserverUtils::InvalidateRenderingObservers(frame);
+      frame->SchedulePaint();
+    }
+    if (hint & nsChangeHint_NeedReflow) {
+      StyleChangeReflow(frame, hint);
+      didReflowThisFrame = true;
+    }
+
+    // Here we need to propagate repaint frame change hint instead of update
+    // opacity layer change hint when we do opacity optimization for SVG.
+    // We can't do it in nsStyleEffects::CalcDifference() just like we do
+    // for the optimization for 0.99 over opacity values since we have no way
+    // to call SVGUtils::CanOptimizeOpacity() there.
+    if ((hint & nsChangeHint_UpdateOpacityLayer) &&
+        SVGUtils::CanOptimizeOpacity(frame)) {
+      hint &= ~nsChangeHint_UpdateOpacityLayer;
+      hint |= nsChangeHint_RepaintFrame;
+    }
+
+    if ((hint & nsChangeHint_UpdateUsesOpacity) && frame->IsTablePart()) {
+      NS_ASSERTION(hint & nsChangeHint_UpdateOpacityLayer,
+                   "should only return UpdateUsesOpacity hint "
+                   "when also returning UpdateOpacityLayer hint");
+      // When an internal table part (including cells) changes between
+      // having opacity 1 and non-1, it changes whether its
+      // backgrounds (and those of table parts inside of it) are
+      // painted as part of the table's nsDisplayTableBorderBackground
+      // display item, or part of its own display item.  That requires
+      // invalidation, so change UpdateOpacityLayer to RepaintFrame.
+      hint &= ~nsChangeHint_UpdateOpacityLayer;
+      hint |= nsChangeHint_RepaintFrame;
+    }
+
+    // Opacity disables preserve-3d, so if we toggle it, then we also need
+    // to update the overflow areas of all potentially affected frames.
+    if ((hint & nsChangeHint_UpdateUsesOpacity) &&
+        frame->StyleDisplay()->mTransformStyle ==
+            StyleTransformStyle::Preserve3d) {
+      hint |= nsChangeHint_UpdateSubtreeOverflow;
+    }
+
+    if (hint & nsChangeHint_UpdateBackgroundPosition) {
+      // For most frame types, DLBI can detect background position changes,
+      // so we only need to schedule a paint.
+      hint |= nsChangeHint_SchedulePaint;
+      if (frame->IsTablePart() || frame->IsMathMLFrame()) {
+        // Table parts and MathML frames don't build display items for their
+        // backgrounds, so DLBI can't detect background-position changes for
+        // these frames. Repaint the whole frame.
+        hint |= nsChangeHint_RepaintFrame;
+      }
+    }
+
+    if (hint &
+        (nsChangeHint_RepaintFrame | nsChangeHint_UpdateOpacityLayer |
+         nsChangeHint_UpdateTransformLayer |
+         nsChangeHint_ChildrenOnlyTransform | nsChangeHint_SchedulePaint)) {
+      ApplyRenderingChangeToTree(presContext->PresShell(), frame, hint);
+    }
+
+    if (hint & (nsChangeHint_UpdateTransformLayer |
+                nsChangeHint_AddOrRemoveTransform)) {
+      // We need to trigger re-snapping to this content if we snapped to the
+      // content on the last scroll operation.
+      ScrollSnapUtils::PostPendingResnapIfNeededFor(frame);
+    }
+
+    if ((hint & nsChangeHint_RecomputePosition) && !didReflowThisFrame) {
+      // It is possible for this to fall back to a reflow
+      if (!RecomputePosition(frame)) {
+        StyleChangeReflow(frame, nsChangeHint_NeedReflow |
+                                     nsChangeHint_ReflowChangesSizeOrPosition);
+        didReflowThisFrame = true;
+      }
+    }
+    NS_ASSERTION(!(hint & nsChangeHint_ChildrenOnlyTransform) ||
+                     (hint & nsChangeHint_UpdateOverflow),
+                 "nsChangeHint_UpdateOverflow should be passed too");
+    if (!didReflowThisFrame &&
+        (hint & (nsChangeHint_UpdateOverflow |
+                 nsChangeHint_UpdatePostTransformOverflow |
+                 nsChangeHint_UpdateParentOverflow |
+                 nsChangeHint_UpdateSubtreeOverflow))) {
+      if (hint & nsChangeHint_UpdateSubtreeOverflow) {
+        for (nsIFrame* cont = frame; cont;
+             cont = nsLayoutUtils::GetNextContinuationOrIBSplitSibling(cont)) {
+          AddSubtreeToOverflowTracker(cont, mOverflowChangedTracker);
+        }
+        // The work we just did in AddSubtreeToOverflowTracker
+        // subsumes some of the other hints:
+        hint &= ~(nsChangeHint_UpdateOverflow |
+                  nsChangeHint_UpdatePostTransformOverflow);
+      }
+      if (hint & nsChangeHint_ChildrenOnlyTransform) {
+        // We need to update overflows. The correct frame(s) to update depends
+        // on whether the ChangeHint came from an outer or an inner svg.
+        nsIFrame* hintFrame = GetFrameForChildrenOnlyTransformHint(frame);
+        NS_ASSERTION(!nsLayoutUtils::GetNextContinuationOrIBSplitSibling(frame),
+                     "SVG frames should not have continuations "
+                     "or ib-split siblings");
+        NS_ASSERTION(
+            !nsLayoutUtils::GetNextContinuationOrIBSplitSibling(hintFrame),
+            "SVG frames should not have continuations "
+            "or ib-split siblings");
+        if (hintFrame->IsSVGOuterSVGAnonChildFrame()) {
+          // The children only transform of an outer svg frame is applied to
+          // the outer svg's anonymous child frame (instead of to the
+          // anonymous child's children).
+
+          if (!CanSkipOverflowUpdates(hintFrame)) {
+            mOverflowChangedTracker.AddFrame(
+                hintFrame, OverflowChangedTracker::CHILDREN_CHANGED);
+          }
+        } else {
+          // The children only transform is applied to the child frames of an
+          // inner svg frame, so update the child overflows.
+          nsIFrame* childFrame = hintFrame->PrincipalChildList().FirstChild();
+          for (; childFrame; childFrame = childFrame->GetNextSibling()) {
+            MOZ_ASSERT(childFrame->IsSVGFrame(),
+                       "Not expecting non-SVG children");
+            if (!CanSkipOverflowUpdates(childFrame)) {
+              mOverflowChangedTracker.AddFrame(
+                  childFrame, OverflowChangedTracker::CHILDREN_CHANGED);
+            }
+            NS_ASSERTION(
+                !nsLayoutUtils::GetNextContinuationOrIBSplitSibling(childFrame),
+                "SVG frames should not have continuations "
+                "or ib-split siblings");
+            NS_ASSERTION(
+                childFrame->GetParent() == hintFrame,
+                "SVG child frame not expected to have different parent");
+          }
+        }
+      }
+      if (!CanSkipOverflowUpdates(frame)) {
+        if (hint & (nsChangeHint_UpdateOverflow |
+                    nsChangeHint_UpdatePostTransformOverflow)) {
+          OverflowChangedTracker::ChangeKind changeKind;
+          // If we have both nsChangeHint_UpdateOverflow and
+          // nsChangeHint_UpdatePostTransformOverflow,
+          // CHILDREN_CHANGED is selected as it is
+          // strictly stronger.
+          if (hint & nsChangeHint_UpdateOverflow) {
+            changeKind = OverflowChangedTracker::CHILDREN_CHANGED;
+          } else {
+            changeKind = OverflowChangedTracker::TRANSFORM_CHANGED;
+          }
+          for (nsIFrame* cont = frame; cont;
+               cont =
+                   nsLayoutUtils::GetNextContinuationOrIBSplitSibling(cont)) {
+            mOverflowChangedTracker.AddFrame(cont, changeKind);
+          }
+        }
+        // UpdateParentOverflow hints need to be processed in addition
+        // to the above, since if the processing of the above hints
+        // yields no change, the update will not propagate to the
+        // parent.
+        if (hint & nsChangeHint_UpdateParentOverflow) {
+          MOZ_ASSERT(frame->GetParent(),
+                     "shouldn't get style hints for the root frame");
+          for (nsIFrame* cont = frame; cont;
+               cont =
+                   nsLayoutUtils::GetNextContinuationOrIBSplitSibling(cont)) {
+            mOverflowChangedTracker.AddFrame(
+                cont->GetParent(), OverflowChangedTracker::CHILDREN_CHANGED);
+          }
+        }
+      }
+    }
+    if ((hint & nsChangeHint_UpdateCursor) && !didUpdateCursor) {
+      presContext->PresShell()->SynthesizeMouseMove(false);
+      didUpdateCursor = true;
+    }
+    if (hint & nsChangeHint_UpdateTableCellSpans) {
+      frameConstructor->UpdateTableCellSpans(content);
+    }
+    if (hint & nsChangeHint_VisibilityChange) {
+      frame->UpdateVisibleDescendantsState();
+    }
+  }
+
+  aChangeList.Clear();
+  FlushOverflowChangedTracker();
+}
+
+/* static */
+uint64_t RestyleManager::GetAnimationGenerationForFrame(nsIFrame* aStyleFrame) {
+  EffectSet* effectSet = EffectSet::GetForStyleFrame(aStyleFrame);
+  return effectSet ? effectSet->GetAnimationGeneration() : 0;
+}
+
+void RestyleManager::IncrementAnimationGeneration() {
+  // We update the animation generation at start of each call to
+  // ProcessPendingRestyles so we should ignore any subsequent (redundant)
+  // calls that occur while we are still processing restyles.
+  if (!mInStyleRefresh) {
+    ++mAnimationGeneration;
+  }
+}
+
+/* static */
+void RestyleManager::AddLayerChangesForAnimation(
+    nsIFrame* aStyleFrame, nsIFrame* aPrimaryFrame, Element* aElement,
+    nsChangeHint aHintForThisFrame, nsStyleChangeList& aChangeListToProcess) {
+  MOZ_ASSERT(aElement);
+  MOZ_ASSERT(!!aStyleFrame == !!aPrimaryFrame);
+  if (!aStyleFrame) {
+    return;
+  }
+
+  uint64_t frameGeneration =
+      RestyleManager::GetAnimationGenerationForFrame(aStyleFrame);
+
+  Maybe<nsCSSPropertyIDSet> effectiveAnimationProperties;
+
+  nsChangeHint hint = nsChangeHint(0);
+  auto maybeApplyChangeHint = [&](const Maybe<uint64_t>& aGeneration,
+                                  DisplayItemType aDisplayItemType) -> bool {
+    if (aGeneration && frameGeneration != *aGeneration) {
+      // If we have a transform layer but don't have any transform style, we
+      // probably just removed the transform but haven't destroyed the layer
+      // yet. In this case we will typically add the appropriate change hint
+      // (nsChangeHint_UpdateContainingBlock) when we compare styles so in
+      // theory we could skip adding any change hint here.
+      //
+      // However, sometimes when we compare styles we'll get no change. For
+      // example, if the transform style was 'none' when we sent the transform
+      // animation to the compositor and the current transform style is now
+      // 'none' we'll think nothing changed but actually we still need to
+      // trigger an update to clear whatever style the transform animation set
+      // on the compositor. To handle this case we simply set all the change
+      // hints relevant to removing transform style (since we don't know exactly
+      // what changes happened while the animation was running on the
+      // compositor).
+      //
+      // Note that we *don't* add nsChangeHint_UpdateTransformLayer since if we
+      // did, ApplyRenderingChangeToTree would complain that we're updating a
+      // transform layer without a transform.
+      if (aDisplayItemType == DisplayItemType::TYPE_TRANSFORM &&
+          !aStyleFrame->StyleDisplay()->HasTransformStyle()) {
+        // Add all the hints for a removing a transform if they are not already
+        // set for this frame.
+        if (!(NS_IsHintSubset(nsChangeHint_ComprehensiveAddOrRemoveTransform,
+                              aHintForThisFrame))) {
+          hint |= nsChangeHint_ComprehensiveAddOrRemoveTransform;
+        }
+        return true;
+      }
+      hint |= LayerAnimationInfo::GetChangeHintFor(aDisplayItemType);
+    }
+
+    // We consider it's the first paint for the frame if we have an animation
+    // for the property but have no layer, for the case of WebRender,  no
+    // corresponding animation info.
+    // Note that in case of animations which has properties preventing running
+    // on the compositor, e.g., width or height, corresponding layer is not
+    // created at all, but even in such cases, we normally set valid change
+    // hint for such animations in each tick, i.e. restyles in each tick. As
+    // a result, we usually do restyles for such animations in every tick on
+    // the main-thread.  The only animations which will be affected by this
+    // explicit change hint are animations that have opacity/transform but did
+    // not have those properies just before. e.g, setting transform by
+    // setKeyframes or changing target element from other target which prevents
+    // running on the compositor, etc.
+    if (!aGeneration) {
+      nsChangeHint hintForDisplayItem =
+          LayerAnimationInfo::GetChangeHintFor(aDisplayItemType);
+      // We don't need to apply the corresponding change hint if we already have
+      // it.
+      if (NS_IsHintSubset(hintForDisplayItem, aHintForThisFrame)) {
+        return true;
+      }
+
+      if (!effectiveAnimationProperties) {
+        effectiveAnimationProperties.emplace(
+            nsLayoutUtils::GetAnimationPropertiesForCompositor(aStyleFrame));
+      }
+      const nsCSSPropertyIDSet& propertiesForDisplayItem =
+          LayerAnimationInfo::GetCSSPropertiesFor(aDisplayItemType);
+      if (effectiveAnimationProperties->Intersects(propertiesForDisplayItem)) {
+        hint |= hintForDisplayItem;
+      }
+    }
+    return true;
+  };
+
+  AnimationInfo::EnumerateGenerationOnFrame(
+      aStyleFrame, aElement, LayerAnimationInfo::sDisplayItemTypes,
+      maybeApplyChangeHint);
+
+  if (hint) {
+    // We apply the hint to the primary frame, not the style frame. Transform
+    // and opacity hints apply to the table wrapper box, not the table box.
+    aChangeListToProcess.AppendChange(aPrimaryFrame, aElement, hint);
+  }
+}
+
+RestyleManager::AnimationsWithDestroyedFrame::AnimationsWithDestroyedFrame(
+    RestyleManager* aRestyleManager)
+    : mRestyleManager(aRestyleManager),
+      mRestorePointer(mRestyleManager->mAnimationsWithDestroyedFrame) {
+  MOZ_ASSERT(!mRestyleManager->mAnimationsWithDestroyedFrame,
+             "shouldn't construct recursively");
+  mRestyleManager->mAnimationsWithDestroyedFrame = this;
+}
+
+void RestyleManager::AnimationsWithDestroyedFrame ::
+    StopAnimationsForElementsWithoutFrames() {
+  StopAnimationsWithoutFrame(mContents, PseudoStyleType::NotPseudo);
+  StopAnimationsWithoutFrame(mBeforeContents, PseudoStyleType::before);
+  StopAnimationsWithoutFrame(mAfterContents, PseudoStyleType::after);
+  StopAnimationsWithoutFrame(mMarkerContents, PseudoStyleType::marker);
+}
+
+void RestyleManager::AnimationsWithDestroyedFrame ::StopAnimationsWithoutFrame(
+    nsTArray<RefPtr<nsIContent>>& aArray, PseudoStyleType aPseudoType) {
+  nsAnimationManager* animationManager =
+      mRestyleManager->PresContext()->AnimationManager();
+  nsTransitionManager* transitionManager =
+      mRestyleManager->PresContext()->TransitionManager();
+  for (nsIContent* content : aArray) {
+    if (aPseudoType == PseudoStyleType::NotPseudo) {
+      if (content->GetPrimaryFrame()) {
+        continue;
+      }
+    } else if (aPseudoType == PseudoStyleType::before) {
+      if (nsLayoutUtils::GetBeforeFrame(content)) {
+        continue;
+      }
+    } else if (aPseudoType == PseudoStyleType::after) {
+      if (nsLayoutUtils::GetAfterFrame(content)) {
+        continue;
+      }
+    } else if (aPseudoType == PseudoStyleType::marker) {
+      if (nsLayoutUtils::GetMarkerFrame(content)) {
+        continue;
+      }
+    }
+    dom::Element* element = content->AsElement();
+
+    animationManager->StopAnimationsForElement(element, aPseudoType);
+    transitionManager->StopAnimationsForElement(element, aPseudoType);
+
+    // All other animations should keep running but not running on the
+    // *compositor* at this point.
+    if (EffectSet* effectSet = EffectSet::Get(element, aPseudoType)) {
+      for (KeyframeEffect* effect : *effectSet) {
+        effect->ResetIsRunningOnCompositor();
+      }
+    }
+  }
+}
+
+#ifdef DEBUG
+static bool IsAnonBox(const nsIFrame* aFrame) {
+  return aFrame->Style()->IsAnonBox();
+}
+
+static const nsIFrame* FirstContinuationOrPartOfIBSplit(
+    const nsIFrame* aFrame) {
+  if (!aFrame) {
+    return nullptr;
+  }
+
+  return nsLayoutUtils::FirstContinuationOrIBSplitSibling(aFrame);
+}
+
+static const nsIFrame* ExpectedOwnerForChild(const nsIFrame* aFrame) {
+  const nsIFrame* parent = aFrame->GetParent();
+  if (aFrame->IsTableFrame()) {
+    MOZ_ASSERT(parent->IsTableWrapperFrame());
+    parent = parent->GetParent();
+  }
+
+  if (IsAnonBox(aFrame) && !aFrame->IsTextFrame()) {
+    if (parent->IsLineFrame()) {
+      parent = parent->GetParent();
+    }
+    return parent->IsViewportFrame() ? nullptr
+                                     : FirstContinuationOrPartOfIBSplit(parent);
+  }
+
+  if (aFrame->IsLineFrame()) {
+    // A ::first-line always ends up here via its block, which is therefore the
+    // right expected owner.  That block can be an
+    // anonymous box.  For example, we could have a ::first-line on a columnated
+    // block; the blockframe is the column-content anonymous box in that case.
+    // So we don't want to end up in the code below, which steps out of anon
+    // boxes.  Just return the parent of the line frame, which is the block.
+    return parent;
+  }
+
+  if (aFrame->IsLetterFrame()) {
+    // Ditto for ::first-letter. A first-letter always arrives here via its
+    // direct parent, except when it's parented to a ::first-line.
+    if (parent->IsLineFrame()) {
+      parent = parent->GetParent();
+    }
+    return FirstContinuationOrPartOfIBSplit(parent);
+  }
+
+  if (parent->IsLetterFrame()) {
+    // Things never have ::first-letter as their expected parent.  Go
+    // on up to the ::first-letter's parent.
+    parent = parent->GetParent();
+  }
+
+  parent = FirstContinuationOrPartOfIBSplit(parent);
+
+  // We've handled already anon boxes, so now we're looking at
+  // a frame of a DOM element or pseudo. Hop through anon and line-boxes
+  // generated by our DOM parent, and go find the owner frame for it.
+  while (parent && (IsAnonBox(parent) || parent->IsLineFrame())) {
+    auto pseudo = parent->Style()->GetPseudoType();
+    if (pseudo == PseudoStyleType::tableWrapper) {
+      const nsIFrame* tableFrame = parent->PrincipalChildList().FirstChild();
+      MOZ_ASSERT(tableFrame->IsTableFrame());
+      // Handle :-moz-table and :-moz-inline-table.
+      parent = IsAnonBox(tableFrame) ? parent->GetParent() : tableFrame;
+    } else {
+      // We get the in-flow parent here so that we can handle the OOF anonymous
+      // boxed to get the correct parent.
+      parent = parent->GetInFlowParent();
+    }
+    parent = FirstContinuationOrPartOfIBSplit(parent);
+  }
+
+  return parent;
+}
+
+// FIXME(emilio, bug 1633685): We should ideally figure out how to properly
+// restyle replicated fixed pos frames... We seem to assume everywhere that they
+// can't get restyled at the moment...
+static bool IsInReplicatedFixedPosTree(const nsIFrame* aFrame) {
+  if (!aFrame->PresContext()->IsPaginated()) {
+    return false;
+  }
+
+  for (; aFrame; aFrame = aFrame->GetParent()) {
+    if (aFrame->StyleDisplay()->mPosition == StylePositionProperty::Fixed &&
+        !aFrame->FirstContinuation()->IsPrimaryFrame() &&
+        nsLayoutUtils::IsReallyFixedPos(aFrame)) {
+      return true;
+    }
+  }
+
+  return true;
+}
+
+void ServoRestyleState::AssertOwner(const ServoRestyleState& aParent) const {
+  MOZ_ASSERT(mOwner);
+  MOZ_ASSERT(!mOwner->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW));
+  MOZ_ASSERT(!mOwner->IsColumnSpanInMulticolSubtree());
+  // We allow aParent.mOwner to be null, for cases when we're not starting at
+  // the root of the tree.  We also allow aParent.mOwner to be somewhere up our
+  // expected owner chain not our immediate owner, which allows us creating long
+  // chains of ServoRestyleStates in some cases where it's just not worth it.
+  if (aParent.mOwner) {
+    const nsIFrame* owner = ExpectedOwnerForChild(mOwner);
+    if (owner != aParent.mOwner && !IsInReplicatedFixedPosTree(mOwner)) {
+      MOZ_ASSERT(IsAnonBox(owner),
+                 "Should only have expected owner weirdness when anon boxes "
+                 "are involved");
+      bool found = false;
+      for (; owner; owner = ExpectedOwnerForChild(owner)) {
+        if (owner == aParent.mOwner) {
+          found = true;
+          break;
+        }
+      }
+      MOZ_ASSERT(found, "Must have aParent.mOwner on our expected owner chain");
+    }
+  }
+}
+
+nsChangeHint ServoRestyleState::ChangesHandledFor(
+    const nsIFrame* aFrame) const {
+  if (!mOwner) {
+    MOZ_ASSERT(!mChangesHandled);
+    return mChangesHandled;
+  }
+
+  MOZ_ASSERT(mOwner == ExpectedOwnerForChild(aFrame) ||
+                 IsInReplicatedFixedPosTree(aFrame),
+             "Missed some frame in the hierarchy?");
+  return mChangesHandled;
+}
+#endif
+
+void ServoRestyleState::AddPendingWrapperRestyle(nsIFrame* aWrapperFrame) {
+  MOZ_ASSERT(aWrapperFrame->Style()->IsWrapperAnonBox(),
+             "All our wrappers are anon boxes, and why would we restyle "
+             "non-inheriting ones?");
+  MOZ_ASSERT(aWrapperFrame->Style()->IsInheritingAnonBox(),
+             "All our wrappers are anon boxes, and why would we restyle "
+             "non-inheriting ones?");
+  MOZ_ASSERT(
+      aWrapperFrame->Style()->GetPseudoType() != PseudoStyleType::cellContent,
+      "Someone should be using TableAwareParentFor");
+  MOZ_ASSERT(
+      aWrapperFrame->Style()->GetPseudoType() != PseudoStyleType::tableWrapper,
+      "Someone should be using TableAwareParentFor");
+  // Make sure we only add first continuations.
+  aWrapperFrame = aWrapperFrame->FirstContinuation();
+  nsIFrame* last = mPendingWrapperRestyles.SafeLastElement(nullptr);
+  if (last == aWrapperFrame) {
+    // Already queued up, nothing to do.
+    return;
+  }
+
+  // Make sure to queue up parents before children.  But don't queue up
+  // ancestors of non-anonymous boxes here; those are handled when we traverse
+  // their non-anonymous kids.
+  if (aWrapperFrame->ParentIsWrapperAnonBox()) {
+    AddPendingWrapperRestyle(TableAwareParentFor(aWrapperFrame));
+  }
+
+  // If the append fails, we'll fail to restyle properly, but that's probably
+  // better than crashing.
+  if (mPendingWrapperRestyles.AppendElement(aWrapperFrame, fallible)) {
+    aWrapperFrame->SetIsWrapperAnonBoxNeedingRestyle(true);
+  }
+}
+
+void ServoRestyleState::ProcessWrapperRestyles(nsIFrame* aParentFrame) {
+  size_t i = mPendingWrapperRestyleOffset;
+  while (i < mPendingWrapperRestyles.Length()) {
+    i += ProcessMaybeNestedWrapperRestyle(aParentFrame, i);
+  }
+
+  mPendingWrapperRestyles.TruncateLength(mPendingWrapperRestyleOffset);
+}
+
+size_t ServoRestyleState::ProcessMaybeNestedWrapperRestyle(nsIFrame* aParent,
+                                                           size_t aIndex) {
+  // The frame at index aIndex is something we should restyle ourselves, but
+  // following frames may need separate ServoRestyleStates to restyle.
+  MOZ_ASSERT(aIndex < mPendingWrapperRestyles.Length());
+
+  nsIFrame* cur = mPendingWrapperRestyles[aIndex];
+  MOZ_ASSERT(cur->Style()->IsWrapperAnonBox());
+
+  // Where is cur supposed to inherit from?  From its parent frame, except in
+  // the case when cur is a table, in which case it should be its grandparent.
+  // Also, not in the case when the resulting frame would be a first-line; in
+  // that case we should be inheriting from the block, and the first-line will
+  // do its fixup later if needed.
+  //
+  // Note that after we do all that fixup the parent we get might still not be
+  // aParent; for example aParent could be a scrollframe, in which case we
+  // should inherit from the scrollcontent frame.  Or the parent might be some
+  // continuation of aParent.
+  //
+  // Try to assert as much as we can about the parent we actually end up using
+  // without triggering bogus asserts in all those various edge cases.
+  nsIFrame* parent = cur->GetParent();
+  if (cur->IsTableFrame()) {
+    MOZ_ASSERT(parent->IsTableWrapperFrame());
+    parent = parent->GetParent();
+  }
+  if (parent->IsLineFrame()) {
+    parent = parent->GetParent();
+  }
+  MOZ_ASSERT(FirstContinuationOrPartOfIBSplit(parent) == aParent ||
+             (parent->Style()->IsInheritingAnonBox() &&
+              parent->GetContent() == aParent->GetContent()));
+
+  // Now "this" is a ServoRestyleState for aParent, so if parent is not a next
+  // continuation (possibly across ib splits) of aParent we need a new
+  // ServoRestyleState for the kid.
+  Maybe<ServoRestyleState> parentRestyleState;
+  nsIFrame* parentForRestyle =
+      nsLayoutUtils::FirstContinuationOrIBSplitSibling(parent);
+  if (parentForRestyle != aParent) {
+    parentRestyleState.emplace(*parentForRestyle, *this, nsChangeHint_Empty,
+                               Type::InFlow);
+  }
+  ServoRestyleState& curRestyleState =
+      parentRestyleState ? *parentRestyleState : *this;
+
+  // This frame may already have been restyled.  Even if it has, we can't just
+  // return, because the next frame may be a kid of it that does need restyling.
+  if (cur->IsWrapperAnonBoxNeedingRestyle()) {
+    parentForRestyle->UpdateStyleOfChildAnonBox(cur, curRestyleState);
+    cur->SetIsWrapperAnonBoxNeedingRestyle(false);
+  }
+
+  size_t numProcessed = 1;
+
+  // Note: no overflow possible here, since aIndex < length.
+  if (aIndex + 1 < mPendingWrapperRestyles.Length()) {
+    nsIFrame* next = mPendingWrapperRestyles[aIndex + 1];
+    if (TableAwareParentFor(next) == cur &&
+        next->IsWrapperAnonBoxNeedingRestyle()) {
+      // It might be nice if we could do better than nsChangeHint_Empty.  On
+      // the other hand, presumably our mChangesHandled already has the bits
+      // we really want here so in practice it doesn't matter.
+      ServoRestyleState childState(*cur, curRestyleState, nsChangeHint_Empty,
+                                   Type::InFlow,
+                                   /* aAssertWrapperRestyleLength = */ false);
+      numProcessed +=
+          childState.ProcessMaybeNestedWrapperRestyle(cur, aIndex + 1);
+    }
+  }
+
+  return numProcessed;
+}
+
+nsIFrame* ServoRestyleState::TableAwareParentFor(const nsIFrame* aChild) {
+  // We want to get the anon box parent for aChild. where aChild has
+  // ParentIsWrapperAnonBox().
+  //
+  // For the most part this is pretty straightforward, but there are two
+  // wrinkles.  First, if aChild is a table, then we really want the parent of
+  // its table wrapper.
+  if (aChild->IsTableFrame()) {
+    aChild = aChild->GetParent();
+    MOZ_ASSERT(aChild->IsTableWrapperFrame());
+  }
+
+  nsIFrame* parent = aChild->GetParent();
+  // Now if parent is a cell-content frame, we actually want the cellframe.
+  if (parent->Style()->GetPseudoType() == PseudoStyleType::cellContent) {
+    parent = parent->GetParent();
+  } else if (parent->IsTableWrapperFrame()) {
+    // Must be a caption.  In that case we want the table here.
+    MOZ_ASSERT(aChild->StyleDisplay()->mDisplay == StyleDisplay::TableCaption);
+    parent = parent->PrincipalChildList().FirstChild();
+  }
+  return parent;
+}
+
+void RestyleManager::PostRestyleEvent(Element* aElement,
+                                      RestyleHint aRestyleHint,
+                                      nsChangeHint aMinChangeHint) {
+  MOZ_ASSERT(!(aMinChangeHint & nsChangeHint_NeutralChange),
+             "Didn't expect explicit change hints to be neutral!");
+  if (MOZ_UNLIKELY(IsDisconnected()) ||
+      MOZ_UNLIKELY(PresContext()->PresShell()->IsDestroying())) {
+    return;
+  }
+
+  // We allow posting restyles from within change hint handling, but not from
+  // within the restyle algorithm itself.
+  MOZ_ASSERT(!ServoStyleSet::IsInServoTraversal());
+
+  if (!aRestyleHint && !aMinChangeHint) {
+    // FIXME(emilio): we should assert against this instead.
+    return;  // Nothing to do.
+  }
+
+  // Assuming the restyle hints will invalidate cached style for
+  // getComputedStyle, since we don't know if any of the restyling that we do
+  // would affect undisplayed elements.
+  if (aRestyleHint) {
+    if (!(aRestyleHint & RestyleHint::ForAnimations())) {
+      mHaveNonAnimationRestyles = true;
+    }
+
+    IncrementUndisplayedRestyleGeneration();
+  }
+
+  // Processing change hints sometimes causes new change hints to be generated,
+  // and very occasionally, additional restyle hints. We collect the change
+  // hints manually to avoid re-traversing the DOM to find them.
+  if (mReentrantChanges && !aRestyleHint) {
+    mReentrantChanges->AppendElement(ReentrantChange{aElement, aMinChangeHint});
+    return;
+  }
+
+  if (aRestyleHint || aMinChangeHint) {
+    Servo_NoteExplicitHints(aElement, aRestyleHint, aMinChangeHint);
+  }
+}
+
+void RestyleManager::PostRestyleEventForAnimations(Element* aElement,
+                                                   PseudoStyleType aPseudoType,
+                                                   RestyleHint aRestyleHint) {
+  Element* elementToRestyle =
+      AnimationUtils::GetElementForRestyle(aElement, aPseudoType);
+
+  if (!elementToRestyle) {
+    // FIXME: Bug 1371107: When reframing happens,
+    // EffectCompositor::mElementsToRestyle still has unbound old pseudo
+    // element. We should drop it.
+    return;
+  }
+
+  mPresContext->TriggeredAnimationRestyle();
+
+  Servo_NoteExplicitHints(elementToRestyle, aRestyleHint, nsChangeHint(0));
+}
+
+void RestyleManager::RebuildAllStyleData(nsChangeHint aExtraHint,
+                                         RestyleHint aRestyleHint) {
+  // NOTE(emilio): The semantics of these methods are quite funny, in the sense
+  // that we're not supposed to need to rebuild the actual stylist data.
+  //
+  // That's handled as part of the MediumFeaturesChanged stuff, if needed.
+  //
+  // Clear the cached style data only if we are guaranteed to process the whole
+  // DOM tree again.
+  //
+  // FIXME(emilio): Decouple this, probably. This probably just wants to reset
+  // the "uses viewport units / uses rem" bits, and _maybe_ clear cached anon
+  // box styles and such... But it doesn't really always need to clear the
+  // initial style of the document and similar...
+  if (aRestyleHint.DefinitelyRecascadesAllSubtree()) {
+    StyleSet()->ClearCachedStyleData();
+  }
+
+  DocumentStyleRootIterator iter(mPresContext->Document());
+  while (Element* root = iter.GetNextStyleRoot()) {
+    PostRestyleEvent(root, aRestyleHint, aExtraHint);
+  }
+
+  // TODO(emilio, bz): Extensions can add/remove stylesheets that can affect
+  // non-inheriting anon boxes. It's not clear if we want to support that, but
+  // if we do, we need to re-selector-match them here.
+}
+
+/* static */
+void RestyleManager::ClearServoDataFromSubtree(Element* aElement,
+                                               IncludeRoot aIncludeRoot) {
+  if (aElement->HasServoData()) {
+    StyleChildrenIterator it(aElement);
+    for (nsIContent* n = it.GetNextChild(); n; n = it.GetNextChild()) {
+      if (n->IsElement()) {
+        ClearServoDataFromSubtree(n->AsElement(), IncludeRoot::Yes);
+      }
+    }
+  }
+
+  if (MOZ_LIKELY(aIncludeRoot == IncludeRoot::Yes)) {
+    aElement->ClearServoData();
+    MOZ_ASSERT(!aElement->HasAnyOfFlags(Element::kAllServoDescendantBits |
+                                        NODE_NEEDS_FRAME));
+    MOZ_ASSERT(aElement != aElement->OwnerDoc()->GetServoRestyleRoot());
+  }
+}
+
+/* static */
+void RestyleManager::ClearRestyleStateFromSubtree(Element* aElement) {
+  if (aElement->HasAnyOfFlags(Element::kAllServoDescendantBits)) {
+    StyleChildrenIterator it(aElement);
+    for (nsIContent* n = it.GetNextChild(); n; n = it.GetNextChild()) {
+      if (n->IsElement()) {
+        ClearRestyleStateFromSubtree(n->AsElement());
+      }
+    }
+  }
+
+  bool wasRestyled = false;
+  Unused << Servo_TakeChangeHint(aElement, &wasRestyled);
+  aElement->UnsetFlags(Element::kAllServoDescendantBits);
+}
+
+/**
+ * This struct takes care of encapsulating some common state that text nodes may
+ * need to track during the post-traversal.
+ *
+ * This is currently used to properly compute change hints when the parent
+ * element of this node is a display: contents node, and also to avoid computing
+ * the style for text children more than once per element.
+ */
+struct RestyleManager::TextPostTraversalState {
+ public:
+  TextPostTraversalState(Element& aParentElement, ComputedStyle* aParentContext,
+                         bool aDisplayContentsParentStyleChanged,
+                         ServoRestyleState& aParentRestyleState)
+      : mParentElement(aParentElement),
+        mParentContext(aParentContext),
+        mParentRestyleState(aParentRestyleState),
+        mStyle(nullptr),
+        mShouldPostHints(aDisplayContentsParentStyleChanged),
+        mShouldComputeHints(aDisplayContentsParentStyleChanged),
+        mComputedHint(nsChangeHint_Empty) {}
+
+  nsStyleChangeList& ChangeList() { return mParentRestyleState.ChangeList(); }
+
+  ComputedStyle& ComputeStyle(nsIContent* aTextNode) {
+    if (!mStyle) {
+      mStyle = mParentRestyleState.StyleSet().ResolveStyleForText(
+          aTextNode, &ParentStyle());
+    }
+    MOZ_ASSERT(mStyle);
+    return *mStyle;
+  }
+
+  void ComputeHintIfNeeded(nsIContent* aContent, nsIFrame* aTextFrame,
+                           ComputedStyle& aNewStyle) {
+    MOZ_ASSERT(aTextFrame);
+    MOZ_ASSERT(aNewStyle.GetPseudoType() == PseudoStyleType::mozText);
+
+    if (MOZ_LIKELY(!mShouldPostHints)) {
+      return;
+    }
+
+    ComputedStyle* oldStyle = aTextFrame->Style();
+    MOZ_ASSERT(oldStyle->GetPseudoType() == PseudoStyleType::mozText);
+
+    // We rely on the fact that all the text children for the same element share
+    // style to avoid recomputing style differences for all of them.
+    //
+    // TODO(emilio): The above may not be true for ::first-{line,letter}, but
+    // we'll cross that bridge when we support those in stylo.
+    if (mShouldComputeHints) {
+      mShouldComputeHints = false;
+      uint32_t equalStructs;
+      mComputedHint = oldStyle->CalcStyleDifference(aNewStyle, &equalStructs);
+      mComputedHint = NS_RemoveSubsumedHints(
+          mComputedHint, mParentRestyleState.ChangesHandledFor(aTextFrame));
+    }
+
+    if (mComputedHint) {
+      mParentRestyleState.ChangeList().AppendChange(aTextFrame, aContent,
+                                                    mComputedHint);
+    }
+  }
+
+ private:
+  ComputedStyle& ParentStyle() {
+    if (!mParentContext) {
+      mLazilyResolvedParentContext =
+          ServoStyleSet::ResolveServoStyle(mParentElement);
+      mParentContext = mLazilyResolvedParentContext;
+    }
+    return *mParentContext;
+  }
+
+  Element& mParentElement;
+  ComputedStyle* mParentContext;
+  RefPtr<ComputedStyle> mLazilyResolvedParentContext;
+  ServoRestyleState& mParentRestyleState;
+  RefPtr<ComputedStyle> mStyle;
+  bool mShouldPostHints;
+  bool mShouldComputeHints;
+  nsChangeHint mComputedHint;
+};
+
+static void UpdateBackdropIfNeeded(nsIFrame* aFrame, ServoStyleSet& aStyleSet,
+                                   nsStyleChangeList& aChangeList) {
+  const nsStyleDisplay* display = aFrame->Style()->StyleDisplay();
+  if (display->mTopLayer != StyleTopLayer::Top) {
+    return;
+  }
+
+  // Elements in the top layer are guaranteed to have absolute or fixed
+  // position per https://fullscreen.spec.whatwg.org/#new-stacking-layer.
+  MOZ_ASSERT(display->IsAbsolutelyPositionedStyle());
+
+  nsIFrame* backdropPlaceholder =
+      aFrame->GetChildList(FrameChildListID::Backdrop).FirstChild();
+  if (!backdropPlaceholder) {
+    return;
+  }
+
+  MOZ_ASSERT(backdropPlaceholder->IsPlaceholderFrame());
+  nsIFrame* backdropFrame =
+      nsPlaceholderFrame::GetRealFrameForPlaceholder(backdropPlaceholder);
+  MOZ_ASSERT(backdropFrame->IsBackdropFrame());
+  MOZ_ASSERT(backdropFrame->Style()->GetPseudoType() ==
+             PseudoStyleType::backdrop);
+
+  RefPtr<ComputedStyle> newStyle = aStyleSet.ResolvePseudoElementStyle(
+      *aFrame->GetContent()->AsElement(), PseudoStyleType::backdrop, nullptr,
+      aFrame->Style());
+
+  // NOTE(emilio): We can't use the changes handled for the owner of the
+  // backdrop frame, since it's out of flow, and parented to the viewport or
+  // canvas frame (depending on the `position` value).
+  MOZ_ASSERT(backdropFrame->GetParent()->IsViewportFrame() ||
+             backdropFrame->GetParent()->IsCanvasFrame());
+  nsTArray<nsIFrame*> wrappersToRestyle;
+  nsTArray<RefPtr<Element>> anchorsToSuppress;
+  ServoRestyleState state(aStyleSet, aChangeList, wrappersToRestyle,
+                          anchorsToSuppress);
+  nsIFrame::UpdateStyleOfOwnedChildFrame(backdropFrame, newStyle, state);
+  MOZ_ASSERT(anchorsToSuppress.IsEmpty());
+}
+
+static void UpdateFirstLetterIfNeeded(nsIFrame* aFrame,
+                                      ServoRestyleState& aRestyleState) {
+  MOZ_ASSERT(
+      !aFrame->IsBlockFrameOrSubclass(),
+      "You're probably duplicating work with UpdatePseudoElementStyles!");
+  if (!aFrame->HasFirstLetterChild()) {
+    return;
+  }
+
+  // We need to find the block the first-letter is associated with so we can
+  // find the right element for the first-letter's style resolution.  Might as
+  // well just delegate the whole thing to that block.
+  nsIFrame* block = aFrame->GetParent();
+  while (!block->IsBlockFrameOrSubclass()) {
+    block = block->GetParent();
+  }
+
+  static_cast<nsBlockFrame*>(block->FirstContinuation())
+      ->UpdateFirstLetterStyle(aRestyleState);
+}
+
+static void UpdateOneAdditionalComputedStyle(nsIFrame* aFrame, uint32_t aIndex,
+                                             ComputedStyle& aOldContext,
+                                             ServoRestyleState& aRestyleState) {
+  auto pseudoType = aOldContext.GetPseudoType();
+  MOZ_ASSERT(pseudoType != PseudoStyleType::NotPseudo);
+  MOZ_ASSERT(
+      !nsCSSPseudoElements::PseudoElementSupportsUserActionState(pseudoType));
+
+  RefPtr<ComputedStyle> newStyle =
+      aRestyleState.StyleSet().ResolvePseudoElementStyle(
+          *aFrame->GetContent()->AsElement(), pseudoType, nullptr,
+          aFrame->Style());
+
+  uint32_t equalStructs;  // Not used, actually.
+  nsChangeHint childHint =
+      aOldContext.CalcStyleDifference(*newStyle, &equalStructs);
+  if (!aFrame->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW) &&
+      !aFrame->IsColumnSpanInMulticolSubtree()) {
+    childHint = NS_RemoveSubsumedHints(childHint,
+                                       aRestyleState.ChangesHandledFor(aFrame));
+  }
+
+  if (childHint) {
+    if (childHint & nsChangeHint_ReconstructFrame) {
+      // If we generate a reconstruct here, remove any non-reconstruct hints we
+      // may have already generated for this content.
+      aRestyleState.ChangeList().PopChangesForContent(aFrame->GetContent());
+    }
+    aRestyleState.ChangeList().AppendChange(aFrame, aFrame->GetContent(),
+                                            childHint);
+  }
+
+  aFrame->SetAdditionalComputedStyle(aIndex, newStyle);
+}
+
+static void UpdateAdditionalComputedStyles(nsIFrame* aFrame,
+                                           ServoRestyleState& aRestyleState) {
+  MOZ_ASSERT(aFrame);
+  MOZ_ASSERT(aFrame->GetContent() && aFrame->GetContent()->IsElement());
+
+  // FIXME(emilio): Consider adding a bit or something to avoid the initial
+  // virtual call?
+  uint32_t index = 0;
+  while (auto* oldStyle = aFrame->GetAdditionalComputedStyle(index)) {
+    UpdateOneAdditionalComputedStyle(aFrame, index++, *oldStyle, aRestyleState);
+  }
+}
+
+static void UpdateFramePseudoElementStyles(nsIFrame* aFrame,
+                                           ServoRestyleState& aRestyleState) {
+  if (nsBlockFrame* blockFrame = do_QueryFrame(aFrame)) {
+    blockFrame->UpdatePseudoElementStyles(aRestyleState);
+  } else {
+    UpdateFirstLetterIfNeeded(aFrame, aRestyleState);
+  }
+
+  UpdateBackdropIfNeeded(aFrame, aRestyleState.StyleSet(),
+                         aRestyleState.ChangeList());
+}
+
+enum class ServoPostTraversalFlags : uint32_t {
+  Empty = 0,
+  // Whether parent was restyled.
+  ParentWasRestyled = 1 << 0,
+  // Skip sending accessibility notifications for all descendants.
+  SkipA11yNotifications = 1 << 1,
+  // Always send accessibility notifications if the element is shown.
+  // The SkipA11yNotifications flag above overrides this flag.
+  SendA11yNotificationsIfShown = 1 << 2,
+};
+
+MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(ServoPostTraversalFlags)
+
+static bool IsVisibleForA11y(const ComputedStyle& aStyle) {
+  return aStyle.StyleVisibility()->IsVisible() && !aStyle.StyleUI()->IsInert();
+}
+
+static bool IsSubtreeVisibleForA11y(const ComputedStyle& aStyle) {
+  return aStyle.StyleDisplay()->mContentVisibility !=
+         StyleContentVisibility::Hidden;
+}
+
+// Send proper accessibility notifications and return post traversal
+// flags for kids.
+static ServoPostTraversalFlags SendA11yNotifications(
+    nsPresContext* aPresContext, Element* aElement,
+    const ComputedStyle& aOldStyle, const ComputedStyle& aNewStyle,
+    ServoPostTraversalFlags aFlags) {
+  using Flags = ServoPostTraversalFlags;
+  MOZ_ASSERT(!(aFlags & Flags::SkipA11yNotifications) ||
+                 !(aFlags & Flags::SendA11yNotificationsIfShown),
+             "The two a11y flags should never be set together");
+
+#ifdef ACCESSIBILITY
+  nsAccessibilityService* accService = GetAccService();
+  if (!accService) {
+    // If we don't have accessibility service, accessibility is not
+    // enabled. Just skip everything.
+    return Flags::Empty;
+  }
+
+  if (aNewStyle.StyleUIReset()->mMozSubtreeHiddenOnlyVisually !=
+      aOldStyle.StyleUIReset()->mMozSubtreeHiddenOnlyVisually) {
+    if (aElement->GetParent() &&
+        aElement->GetParent()->IsXULElement(nsGkAtoms::tabpanels)) {
+      accService->NotifyOfTabPanelVisibilityChange(
+          aPresContext->PresShell(), aElement,
+          aNewStyle.StyleUIReset()->mMozSubtreeHiddenOnlyVisually);
+    }
+  }
+
+  if (aFlags & Flags::SkipA11yNotifications) {
+    // Propagate the skipping flag to descendants.
+    return Flags::SkipA11yNotifications;
+  }
+
+  bool needsNotify = false;
+  const bool isVisible = IsVisibleForA11y(aNewStyle);
+  const bool wasVisible = IsVisibleForA11y(aOldStyle);
+
+  if (aFlags & Flags::SendA11yNotificationsIfShown) {
+    if (!isVisible) {
+      // Propagate the sending-if-shown flag to descendants.
+      return Flags::SendA11yNotificationsIfShown;
+    }
+    // We have asked accessibility service to remove the whole subtree
+    // of element which becomes invisible from the accessible tree, but
+    // this element is visible, so we need to add it back.
+    needsNotify = true;
+  } else {
+    // If we shouldn't skip in any case, we need to check whether our own
+    // visibility has changed.
+    // Also notify if the subtree visibility change due to content-visibility.
+    const bool isSubtreeVisible = IsSubtreeVisibleForA11y(aNewStyle);
+    const bool wasSubtreeVisible = IsSubtreeVisibleForA11y(aOldStyle);
+    needsNotify =
+        wasVisible != isVisible || wasSubtreeVisible != isSubtreeVisible;
+  }
+
+  if (needsNotify) {
+    PresShell* presShell = aPresContext->PresShell();
+    if (isVisible) {
+      accService->ContentRangeInserted(presShell, aElement,
+                                       aElement->GetNextSibling());
+      // We are adding the subtree. Accessibility service would handle
+      // descendants, so we should just skip them from notifying.
+      return Flags::SkipA11yNotifications;
+    }
+    if (wasVisible) {
+      // Remove the subtree of this invisible element, and ask any shown
+      // descendant to add themselves back.
+      accService->ContentRemoved(presShell, aElement);
+      return Flags::SendA11yNotificationsIfShown;
+    }
+  }
+#endif
+
+  return Flags::Empty;
+}
+
+bool RestyleManager::ProcessPostTraversal(Element* aElement,
+                                          ServoRestyleState& aRestyleState,
+                                          ServoPostTraversalFlags aFlags) {
+  nsIFrame* styleFrame = nsLayoutUtils::GetStyleFrame(aElement);
+  nsIFrame* primaryFrame = aElement->GetPrimaryFrame();
+
+  MOZ_DIAGNOSTIC_ASSERT(aElement->HasServoData(),
+                        "Element without Servo data on a post-traversal? How?");
+
+  // NOTE(emilio): This is needed because for table frames the bit is set on the
+  // table wrapper (which is the primary frame), not on the table itself.
+  const bool isOutOfFlow =
+      primaryFrame && primaryFrame->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW);
+
+  // We need this because any column-spanner's parent frame is not its DOM
+  // parent's primary frame. We need some special check similar to out-of-flow
+  // frames.
+  const bool isColumnSpan =
+      primaryFrame && primaryFrame->IsColumnSpanInMulticolSubtree();
+
+  // Grab the change hint from Servo.
+  bool wasRestyled = false;
+  nsChangeHint changeHint =
+      static_cast<nsChangeHint>(Servo_TakeChangeHint(aElement, &wasRestyled));
+
+  RefPtr<ComputedStyle> upToDateStyleIfRestyled =
+      wasRestyled ? ServoStyleSet::ResolveServoStyle(*aElement) : nullptr;
+
+  // We should really fix the weird primary frame mapping for image maps
+  // (bug 135040)...
+  if (styleFrame && styleFrame->GetContent() != aElement) {
+    MOZ_ASSERT(styleFrame->IsImageFrameOrSubclass());
+    styleFrame = nullptr;
+  }
+
+  // Handle lazy frame construction by posting a reconstruct for any lazily-
+  // constructed roots.
+  if (aElement->HasFlag(NODE_NEEDS_FRAME)) {
+    changeHint |= nsChangeHint_ReconstructFrame;
+    MOZ_ASSERT(!styleFrame);
+  }
+
+  if (styleFrame) {
+    MOZ_ASSERT(primaryFrame);
+
+    nsIFrame* maybeAnonBoxChild;
+    if (isOutOfFlow) {
+      maybeAnonBoxChild = primaryFrame->GetPlaceholderFrame();
+    } else {
+      maybeAnonBoxChild = primaryFrame;
+      // Do not subsume change hints for the column-spanner.
+      if (!isColumnSpan) {
+        changeHint = NS_RemoveSubsumedHints(
+            changeHint, aRestyleState.ChangesHandledFor(styleFrame));
+      }
+    }
+
+    // If the parent wasn't restyled, the styles of our anon box parents won't
+    // change either.
+    if ((aFlags & ServoPostTraversalFlags::ParentWasRestyled) &&
+        maybeAnonBoxChild->ParentIsWrapperAnonBox()) {
+      aRestyleState.AddPendingWrapperRestyle(
+          ServoRestyleState::TableAwareParentFor(maybeAnonBoxChild));
+    }
+
+    // If we don't have a ::marker pseudo-element, but need it, then
+    // reconstruct the frame.  (The opposite situation implies 'display'
+    // changes so doesn't need to be handled explicitly here.)
+    if (wasRestyled && styleFrame->StyleDisplay()->IsListItem() &&
+        styleFrame->IsBlockFrameOrSubclass() &&
+        !nsLayoutUtils::GetMarkerPseudo(aElement)) {
+      RefPtr<ComputedStyle> pseudoStyle =
+          aRestyleState.StyleSet().ProbePseudoElementStyle(
+              *aElement, PseudoStyleType::marker, nullptr,
+              upToDateStyleIfRestyled);
+      if (pseudoStyle) {
+        changeHint |= nsChangeHint_ReconstructFrame;
+      }
+    }
+  }
+
+  // Although we shouldn't generate non-ReconstructFrame hints for elements with
+  // no frames, we can still get them here if they were explicitly posted by
+  // PostRestyleEvent, such as a RepaintFrame hint when a :link changes to be
+  // :visited.  Skip processing these hints if there is no frame.
+  if ((styleFrame || (changeHint & nsChangeHint_ReconstructFrame)) &&
+      changeHint) {
+    aRestyleState.ChangeList().AppendChange(styleFrame, aElement, changeHint);
+  }
+
+  // If our change hint is reconstruct, we delegate to the frame constructor,
+  // which consumes the new style and expects the old style to be on the frame.
+  //
+  // XXXbholley: We should teach the frame constructor how to clear the dirty
+  // descendants bit to avoid the traversal here.
+  if (changeHint & nsChangeHint_ReconstructFrame) {
+    if (wasRestyled &&
+        StaticPrefs::layout_css_scroll_anchoring_suppressions_enabled()) {
+      const bool wasAbsPos =
+          styleFrame &&
+          styleFrame->StyleDisplay()->IsAbsolutelyPositionedStyle();
+      auto* newDisp = upToDateStyleIfRestyled->StyleDisplay();
+      // https://drafts.csswg.org/css-scroll-anchoring/#suppression-triggers
+      //
+      // We need to do the position check here rather than in
+      // DidSetComputedStyle because changing position reframes.
+      //
+      // We suppress adjustments whenever we change from being display: none to
+      // be an abspos.
+      //
+      // Similarly, for other changes from abspos to non-abspos styles.
+      //
+      // TODO(emilio): I _think_ chrome won't suppress adjustments whenever
+      // `display` changes. But that causes some infinite loops in cases like
+      // bug 1568778.
+      if (wasAbsPos != newDisp->IsAbsolutelyPositionedStyle()) {
+        aRestyleState.AddPendingScrollAnchorSuppression(aElement);
+      }
+    }
+    ClearRestyleStateFromSubtree(aElement);
+    return true;
+  }
+
+  // TODO(emilio): We could avoid some refcount traffic here, specially in the
+  // ComputedStyle case, which uses atomic refcounting.
+  //
+  // Hold the ComputedStyle alive, because it could become a dangling pointer
+  // during the replacement. In practice it's not a huge deal, but better not
+  // playing with dangling pointers if not needed.
+  //
+  // NOTE(emilio): We could keep around the old computed style for display:
+  // contents elements too, but we don't really need it right now.
+  RefPtr<ComputedStyle> oldOrDisplayContentsStyle =
+      styleFrame ? styleFrame->Style() : nullptr;
+
+  MOZ_ASSERT(!(styleFrame && Servo_Element_IsDisplayContents(aElement)),
+             "display: contents node has a frame, yet we didn't reframe it"
+             " above?");
+  const bool isDisplayContents = !styleFrame && aElement->HasServoData() &&
+                                 Servo_Element_IsDisplayContents(aElement);
+  if (isDisplayContents) {
+    oldOrDisplayContentsStyle = ServoStyleSet::ResolveServoStyle(*aElement);
+  }
+
+  Maybe<ServoRestyleState> thisFrameRestyleState;
+  if (styleFrame) {
+    auto type = isOutOfFlow || isColumnSpan ? ServoRestyleState::Type::OutOfFlow
+                                            : ServoRestyleState::Type::InFlow;
+
+    thisFrameRestyleState.emplace(*styleFrame, aRestyleState, changeHint, type);
+  }
+
+  // We can't really assume as used changes from display: contents elements (or
+  // other elements without frames).
+  ServoRestyleState& childrenRestyleState =
+      thisFrameRestyleState ? *thisFrameRestyleState : aRestyleState;
+
+  ComputedStyle* upToDateStyle =
+      wasRestyled ? upToDateStyleIfRestyled : oldOrDisplayContentsStyle;
+
+  ServoPostTraversalFlags childrenFlags =
+      wasRestyled ? ServoPostTraversalFlags::ParentWasRestyled
+                  : ServoPostTraversalFlags::Empty;
+
+  if (wasRestyled && oldOrDisplayContentsStyle) {
+    MOZ_ASSERT(styleFrame || isDisplayContents);
+
+    // We want to walk all the continuations here, even the ones with different
+    // styles.  In practice, the only reason we get continuations with different
+    // styles here is ::first-line (::first-letter never affects element
+    // styles).  But in that case, newStyle is the right context for the
+    // _later_ continuations anyway (the ones not affected by ::first-line), not
+    // the earlier ones, so there is no point stopping right at the point when
+    // we'd actually be setting the right ComputedStyle.
+    //
+    // This does mean that we may be setting the wrong ComputedStyle on our
+    // initial continuations; ::first-line fixes that up after the fact.
+    for (nsIFrame* f = styleFrame; f; f = f->GetNextContinuation()) {
+      MOZ_ASSERT_IF(f != styleFrame, !f->GetAdditionalComputedStyle(0));
+      f->SetComputedStyle(upToDateStyle);
+    }
+
+    if (styleFrame) {
+      UpdateAdditionalComputedStyles(styleFrame, aRestyleState);
+    }
+
+    if (!aElement->GetParent()) {
+      // This is the root.  Update styles on the viewport as needed.
+      ViewportFrame* viewport =
+          do_QueryFrame(mPresContext->PresShell()->GetRootFrame());
+      if (viewport) {
+        // NB: The root restyle state, not the one for our children!
+        viewport->UpdateStyle(aRestyleState);
+      }
+    }
+
+    // Some changes to animations don't affect the computed style and yet still
+    // require the layer to be updated. For example, pausing an animation via
+    // the Web Animations API won't affect an element's style but still
+    // requires to update the animation on the layer.
+    //
+    // We can sometimes reach this when the animated style is being removed.
+    // Since AddLayerChangesForAnimation checks if |styleFrame| has a transform
+    // style or not, we need to call it *after* setting |newStyle| to
+    // |styleFrame| to ensure the animated transform has been removed first.
+    AddLayerChangesForAnimation(styleFrame, primaryFrame, aElement, changeHint,
+                                aRestyleState.ChangeList());
+
+    childrenFlags |= SendA11yNotifications(mPresContext, aElement,
+                                           *oldOrDisplayContentsStyle,
+                                           *upToDateStyle, aFlags);
+  }
+
+  const bool traverseElementChildren =
+      aElement->HasAnyOfFlags(Element::kAllServoDescendantBits);
+  const bool traverseTextChildren =
+      wasRestyled || aElement->HasFlag(NODE_DESCENDANTS_NEED_FRAMES);
+  bool recreatedAnyContext = wasRestyled;
+  if (traverseElementChildren || traverseTextChildren) {
+    StyleChildrenIterator it(aElement);
+    TextPostTraversalState textState(*aElement, upToDateStyle,
+                                     isDisplayContents && wasRestyled,
+                                     childrenRestyleState);
+    for (nsIContent* n = it.GetNextChild(); n; n = it.GetNextChild()) {
+      if (traverseElementChildren && n->IsElement()) {
+        recreatedAnyContext |= ProcessPostTraversal(
+            n->AsElement(), childrenRestyleState, childrenFlags);
+      } else if (traverseTextChildren && n->IsText()) {
+        recreatedAnyContext |= ProcessPostTraversalForText(
+            n, textState, childrenRestyleState, childrenFlags);
+      }
+    }
+  }
+
+  // We want to update frame pseudo-element styles after we've traversed our
+  // kids, because some of those updates (::first-line/::first-letter) need to
+  // modify the styles of the kids, and the child traversal above would just
+  // clobber those modifications.
+  if (styleFrame) {
+    if (wasRestyled) {
+      // Make sure to update anon boxes and pseudo bits after updating text,
+      // otherwise ProcessPostTraversalForText could clobber first-letter
+      // styles, for example.
+      styleFrame->UpdateStyleOfOwnedAnonBoxes(childrenRestyleState);
+    }
+    // Process anon box wrapper frames before ::first-line bits, but _after_
+    // owned anon boxes, since the children wrapper anon boxes could be
+    // inheriting from our own owned anon boxes.
+    childrenRestyleState.ProcessWrapperRestyles(styleFrame);
+    if (wasRestyled) {
+      UpdateFramePseudoElementStyles(styleFrame, childrenRestyleState);
+    } else if (traverseElementChildren &&
+               styleFrame->IsBlockFrameOrSubclass()) {
+      // Even if we were not restyled, if we're a block with a first-line and
+      // one of our descendant elements which is on the first line was restyled,
+      // we need to update the styles of things on the first line, because
+      // they're wrong now.
+      //
+      // FIXME(bz) Could we do better here?  For example, could we keep track of
+      // frames that are "block with a ::first-line so we could avoid
+      // IsFrameOfType() and digging about for the first-line frame if not?
+      // Could we keep track of whether the element children we actually restyle
+      // are affected by first-line?  Something else?  Bug 1385443 tracks making
+      // this better.
+      nsIFrame* firstLineFrame =
+          static_cast<nsBlockFrame*>(styleFrame)->GetFirstLineFrame();
+      if (firstLineFrame) {
+        for (nsIFrame* kid : firstLineFrame->PrincipalChildList()) {
+          ReparentComputedStyleForFirstLine(kid);
+        }
+      }
+    }
+  }
+
+  aElement->UnsetFlags(Element::kAllServoDescendantBits);
+  return recreatedAnyContext;
+}
+
+bool RestyleManager::ProcessPostTraversalForText(
+    nsIContent* aTextNode, TextPostTraversalState& aPostTraversalState,
+    ServoRestyleState& aRestyleState, ServoPostTraversalFlags aFlags) {
+  // Handle lazy frame construction.
+  if (aTextNode->HasFlag(NODE_NEEDS_FRAME)) {
+    aPostTraversalState.ChangeList().AppendChange(
+        nullptr, aTextNode, nsChangeHint_ReconstructFrame);
+    return true;
+  }
+
+  // Handle restyle.
+  nsIFrame* primaryFrame = aTextNode->GetPrimaryFrame();
+  if (!primaryFrame) {
+    return false;
+  }
+
+  // If the parent wasn't restyled, the styles of our anon box parents won't
+  // change either.
+  if ((aFlags & ServoPostTraversalFlags::ParentWasRestyled) &&
+      primaryFrame->ParentIsWrapperAnonBox()) {
+    aRestyleState.AddPendingWrapperRestyle(
+        ServoRestyleState::TableAwareParentFor(primaryFrame));
+  }
+
+  ComputedStyle& newStyle = aPostTraversalState.ComputeStyle(aTextNode);
+  aPostTraversalState.ComputeHintIfNeeded(aTextNode, primaryFrame, newStyle);
+
+  // We want to walk all the continuations here, even the ones with different
+  // styles.  In practice, the only reasons we get continuations with different
+  // styles are ::first-line and ::first-letter.  But in those cases,
+  // newStyle is the right context for the _later_ continuations anyway (the
+  // ones not affected by ::first-line/::first-letter), not the earlier ones,
+  // so there is no point stopping right at the point when we'd actually be
+  // setting the right ComputedStyle.
+  //
+  // This does mean that we may be setting the wrong ComputedStyle on our
+  // initial continuations; ::first-line/::first-letter fix that up after the
+  // fact.
+  for (nsIFrame* f = primaryFrame; f; f = f->GetNextContinuation()) {
+    f->SetComputedStyle(&newStyle);
+  }
+
+  return true;
+}
+
+void RestyleManager::ClearSnapshots() {
+  for (auto iter = mSnapshots.Iter(); !iter.Done(); iter.Next()) {
+    iter.Key()->UnsetFlags(ELEMENT_HAS_SNAPSHOT | ELEMENT_HANDLED_SNAPSHOT);
+    iter.Remove();
+  }
+}
+
+ServoElementSnapshot& RestyleManager::SnapshotFor(Element& aElement) {
+  MOZ_DIAGNOSTIC_ASSERT(!mInStyleRefresh);
+
+  // NOTE(emilio): We can handle snapshots from a one-off restyle of those that
+  // we do to restyle stuff for reconstruction, for example.
+  //
+  // It seems to be the case that we always flush in between that happens and
+  // the next attribute change, so we can assert that we haven't handled the
+  // snapshot here yet. If this assertion didn't hold, we'd need to unset that
+  // flag from here too.
+  //
+  // Can't wait to make ProcessPendingRestyles the only entry-point for styling,
+  // so this becomes much easier to reason about. Today is not that day though.
+  MOZ_ASSERT(!aElement.HasFlag(ELEMENT_HANDLED_SNAPSHOT));
+
+  ServoElementSnapshot* snapshot =
+      mSnapshots.GetOrInsertNew(&aElement, aElement);
+  aElement.SetFlags(ELEMENT_HAS_SNAPSHOT);
+
+  // Now that we have a snapshot, make sure a restyle is triggered.
+  aElement.NoteDirtyForServo();
+  return *snapshot;
+}
+
+void RestyleManager::DoProcessPendingRestyles(ServoTraversalFlags aFlags) {
+  nsPresContext* presContext = PresContext();
+  PresShell* presShell = presContext->PresShell();
+
+  MOZ_ASSERT(presContext->Document(), "No document?  Pshaw!");
+  // FIXME(emilio): In the "flush animations" case, ideally, we should only
+  // recascade animation styles running on the compositor, so we shouldn't care
+  // about other styles, or new rules that apply to the page...
+  //
+  // However, that's not true as of right now, see bug 1388031 and bug 1388692.
+  MOZ_ASSERT((aFlags & ServoTraversalFlags::FlushThrottledAnimations) ||
+                 !presContext->HasPendingMediaQueryUpdates(),
+             "Someone forgot to update media queries?");
+  MOZ_ASSERT(!nsContentUtils::IsSafeToRunScript(), "Missing a script blocker!");
+  MOZ_RELEASE_ASSERT(!mInStyleRefresh, "Reentrant call?");
+
+  if (MOZ_UNLIKELY(!presShell->DidInitialize())) {
+    // PresShell::FlushPendingNotifications doesn't early-return in the case
+    // where the PresShell hasn't yet been initialized (and therefore we haven't
+    // yet done the initial style traversal of the DOM tree). We should arguably
+    // fix up the callers and assert against this case, but we just detect and
+    // handle it for now.
+    return;
+  }
+
+  // It'd be bad!
+  PresShell::AutoAssertNoFlush noReentrantFlush(*presShell);
+
+  // Create a AnimationsWithDestroyedFrame during restyling process to
+  // stop animations and transitions on elements that have no frame at the end
+  // of the restyling process.
+  AnimationsWithDestroyedFrame animationsWithDestroyedFrame(this);
+
+  ServoStyleSet* styleSet = StyleSet();
+  Document* doc = presContext->Document();
+
+  // Ensure the refresh driver is active during traversal to avoid mutating
+  // mActiveTimer and mMostRecentRefresh time.
+  presContext->RefreshDriver()->MostRecentRefresh();
+
+  if (!doc->GetServoRestyleRoot()) {
+    // This might post new restyles, so need to do it here. Don't do it if we're
+    // already going to restyle tho, so that we don't potentially reflow with
+    // dirty styling.
+    presContext->UpdateContainerQueryStyles();
+    presContext->FinishedContainerQueryUpdate();
+  }
+
+  // Perform the Servo traversal, and the post-traversal if required. We do this
+  // in a loop because certain rare paths in the frame constructor can trigger
+  // additional style invalidations.
+  //
+  // FIXME(emilio): Confirm whether that's still true now that XBL is gone.
+  mInStyleRefresh = true;
+  if (mHaveNonAnimationRestyles) {
+    ++mAnimationGeneration;
+  }
+
+  if (mRestyleForCSSRuleChanges) {
+    aFlags |= ServoTraversalFlags::ForCSSRuleChanges;
+  }
+
+  while (styleSet->StyleDocument(aFlags)) {
+    ClearSnapshots();
+
+    // Select scroll anchors for frames that have been scrolled. Do this
+    // before processing restyled frames so that anchor nodes are correctly
+    // marked when directly moving frames with RecomputePosition.
+    presContext->PresShell()->FlushPendingScrollAnchorSelections();
+
+    nsStyleChangeList currentChanges;
+    bool anyStyleChanged = false;
+
+    // Recreate styles , and queue up change hints (which also handle lazy frame
+    // construction).
+    nsTArray<RefPtr<Element>> anchorsToSuppress;
+
+    {
+      DocumentStyleRootIterator iter(doc->GetServoRestyleRoot());
+      while (Element* root = iter.GetNextStyleRoot()) {
+        nsTArray<nsIFrame*> wrappersToRestyle;
+        ServoRestyleState state(*styleSet, currentChanges, wrappersToRestyle,
+                                anchorsToSuppress);
+        ServoPostTraversalFlags flags = ServoPostTraversalFlags::Empty;
+        anyStyleChanged |= ProcessPostTraversal(root, state, flags);
+      }
+
+      // We want to suppress adjustments the current (before-change) scroll
+      // anchor container now, and save a reference to the content node so that
+      // we can suppress them in the after-change scroll anchor .
+      for (Element* element : anchorsToSuppress) {
+        if (nsIFrame* frame = element->GetPrimaryFrame()) {
+          if (auto* container = ScrollAnchorContainer::FindFor(frame)) {
+            container->SuppressAdjustments();
+          }
+        }
+      }
+    }
+
+    doc->ClearServoRestyleRoot();
+    ClearSnapshots();
+
+    // Process the change hints.
+    //
+    // Unfortunately, the frame constructor can generate new change hints while
+    // processing existing ones. We redirect those into a secondary queue and
+    // iterate until there's nothing left.
+    {
+      ReentrantChangeList newChanges;
+      mReentrantChanges = &newChanges;
+      while (!currentChanges.IsEmpty()) {
+        ProcessRestyledFrames(currentChanges);
+        MOZ_ASSERT(currentChanges.IsEmpty());
+        for (ReentrantChange& change : newChanges) {
+          if (!(change.mHint & nsChangeHint_ReconstructFrame) &&
+              !change.mContent->GetPrimaryFrame()) {
+            // SVG Elements post change hints without ensuring that the primary
+            // frame will be there after that (see bug 1366142).
+            //
+            // Just ignore those, since we can't really process them.
+            continue;
+          }
+          currentChanges.AppendChange(change.mContent->GetPrimaryFrame(),
+                                      change.mContent, change.mHint);
+        }
+        newChanges.Clear();
+      }
+      mReentrantChanges = nullptr;
+    }
+
+    // Suppress adjustments in the after-change scroll anchors if needed, now
+    // that we're done reframing everything.
+    for (Element* element : anchorsToSuppress) {
+      if (nsIFrame* frame = element->GetPrimaryFrame()) {
+        if (auto* container = ScrollAnchorContainer::FindFor(frame)) {
+          container->SuppressAdjustments();
+        }
+      }
+    }
+
+    if (anyStyleChanged) {
+      // Maybe no styles changed when:
+      //
+      //  * Only explicit change hints were posted in the first place.
+      //  * When an attribute or state change in the content happens not to need
+      //    a restyle after all.
+      //
+      // In any case, we don't need to increment the restyle generation in that
+      // case.
+      IncrementRestyleGeneration();
+    }
+
+    mInStyleRefresh = false;
+    presContext->UpdateContainerQueryStyles();
+    mInStyleRefresh = true;
+  }
+
+  doc->ClearServoRestyleRoot();
+  presContext->FinishedContainerQueryUpdate();
+  presContext->UpdateHiddenByContentVisibilityForAnimationsIfNeeded();
+  ClearSnapshots();
+  styleSet->AssertTreeIsClean();
+
+  mHaveNonAnimationRestyles = false;
+  mRestyleForCSSRuleChanges = false;
+  mInStyleRefresh = false;
+
+  // Now that everything has settled, see if we have enough free rule nodes in
+  // the tree to warrant sweeping them.
+  styleSet->MaybeGCRuleTree();
+
+  // Note: We are in the scope of |animationsWithDestroyedFrame|, so
+  //       |mAnimationsWithDestroyedFrame| is still valid.
+  MOZ_ASSERT(mAnimationsWithDestroyedFrame);
+  mAnimationsWithDestroyedFrame->StopAnimationsForElementsWithoutFrames();
+}
+
+#ifdef DEBUG
+static void VerifyFlatTree(const nsIContent& aContent) {
+  StyleChildrenIterator iter(&aContent);
+
+  for (auto* content = iter.GetNextChild(); content;
+       content = iter.GetNextChild()) {
+    MOZ_ASSERT(content->GetFlattenedTreeParentNodeForStyle() == &aContent);
+    VerifyFlatTree(*content);
+  }
+}
+#endif
+
+void RestyleManager::ProcessPendingRestyles() {
+  AUTO_PROFILER_LABEL_RELEVANT_FOR_JS("Styles", LAYOUT);
+#ifdef DEBUG
+  if (auto* root = mPresContext->Document()->GetRootElement()) {
+    VerifyFlatTree(*root);
+  }
+#endif
+
+  DoProcessPendingRestyles(ServoTraversalFlags::Empty);
+}
+
+void RestyleManager::ProcessAllPendingAttributeAndStateInvalidations() {
+  if (mSnapshots.IsEmpty()) {
+    return;
+  }
+  for (const auto& key : mSnapshots.Keys()) {
+    // Servo data for the element might have been dropped. (e.g. by removing
+    // from its document)
+    if (key->HasFlag(ELEMENT_HAS_SNAPSHOT)) {
+      Servo_ProcessInvalidations(StyleSet()->RawData(), key, &mSnapshots);
+    }
+  }
+  ClearSnapshots();
+}
+
+void RestyleManager::UpdateOnlyAnimationStyles() {
+  bool doCSS = PresContext()->EffectCompositor()->HasPendingStyleUpdates();
+  if (!doCSS) {
+    return;
+  }
+
+  DoProcessPendingRestyles(ServoTraversalFlags::FlushThrottledAnimations);
+}
+
+void RestyleManager::ElementStateChanged(Element* aElement,
+                                         ElementState aChangedBits) {
+#ifdef EARLY_BETA_OR_EARLIER
+  if (MOZ_UNLIKELY(mInStyleRefresh)) {
+    MOZ_CRASH_UNSAFE_PRINTF(
+        "Element state change during style refresh (%" PRIu64 ")",
+        aChangedBits.GetInternalValue());
+  }
+#endif
+
+  const ElementState kVisitedAndUnvisited =
+      ElementState::VISITED | ElementState::UNVISITED;
+
+  // We'll restyle when the relevant visited query finishes, regardless of the
+  // style (see Link::VisitedQueryFinished). So there's no need to do anything
+  // as a result of this state change just yet.
+  //
+  // Note that this check checks for _both_ bits: This is only true when visited
+  // changes to unvisited or vice-versa, but not when we start or stop being a
+  // link itself.
+  if (aChangedBits.HasAllStates(kVisitedAndUnvisited)) {
+    aChangedBits &= ~kVisitedAndUnvisited;
+    if (aChangedBits.IsEmpty()) {
+      return;
+    }
+  }
+
+  if (auto changeHint = ChangeForContentStateChange(*aElement, aChangedBits)) {
+    Servo_NoteExplicitHints(aElement, RestyleHint{0}, changeHint);
+  }
+
+  // Don't bother taking a snapshot if no rules depend on these state bits.
+  //
+  // We always take a snapshot for the LTR/RTL event states, since Servo doesn't
+  // track those bits in the same way, and we know that :dir() rules are always
+  // present in UA style sheets.
+  if (!aChangedBits.HasAtLeastOneOfStates(ElementState::DIR_STATES) &&
+      !StyleSet()->HasStateDependency(*aElement, aChangedBits)) {
+    return;
+  }
+
+  // Assuming we need to invalidate cached style in getComputedStyle for
+  // undisplayed elements, since we don't know if it is needed.
+  IncrementUndisplayedRestyleGeneration();
+
+  if (!aElement->HasServoData() &&
+      !(aElement->GetSelectorFlags() &
+        NodeSelectorFlags::RelativeSelectorSearchDirectionAncestorSibling)) {
+    return;
+  }
+
+  ServoElementSnapshot& snapshot = SnapshotFor(*aElement);
+  ElementState previousState = aElement->StyleState() ^ aChangedBits;
+  snapshot.AddState(previousState);
+
+  ServoStyleSet& styleSet = *StyleSet();
+  MaybeRestyleForNthOfState(styleSet, aElement, aChangedBits);
+  MaybeRestyleForRelativeSelectorState(styleSet, aElement, aChangedBits);
+}
+
+void RestyleManager::MaybeRestyleForNthOfState(ServoStyleSet& aStyleSet,
+                                               Element* aChild,
+                                               ElementState aChangedBits) {
+  const auto* parentNode = aChild->GetParentNode();
+  MOZ_ASSERT(parentNode);
+  const auto parentFlags = parentNode->GetSelectorFlags();
+  if (!(parentFlags & NodeSelectorFlags::HasSlowSelectorNthOf)) {
+    return;
+  }
+
+  if (aStyleSet.HasNthOfStateDependency(*aChild, aChangedBits)) {
+    RestyleSiblingsForNthOf(aChild, parentFlags);
+  }
+}
+
+static inline bool AttributeInfluencesOtherPseudoClassState(
+    const Element& aElement, const nsAtom* aAttribute) {
+  // We must record some state for :-moz-browser-frame,
+  // :-moz-table-border-nonzero, and :-moz-select-list-box.
+  if (aAttribute == nsGkAtoms::mozbrowser) {
+    return aElement.IsAnyOfHTMLElements(nsGkAtoms::iframe, nsGkAtoms::frame);
+  }
+
+  if (aAttribute == nsGkAtoms::border) {
+    return aElement.IsHTMLElement(nsGkAtoms::table);
+  }
+
+  if (aAttribute == nsGkAtoms::multiple || aAttribute == nsGkAtoms::size) {
+    return aElement.IsHTMLElement(nsGkAtoms::select);
+  }
+
+  return false;
+}
+
+static inline bool NeedToRecordAttrChange(
+    const ServoStyleSet& aStyleSet, const Element& aElement,
+    int32_t aNameSpaceID, nsAtom* aAttribute,
+    bool* aInfluencesOtherPseudoClassState) {
+  *aInfluencesOtherPseudoClassState =
+      AttributeInfluencesOtherPseudoClassState(aElement, aAttribute);
+
+  // If the attribute influences one of the pseudo-classes that are backed by
+  // attributes, we just record it.
+  if (*aInfluencesOtherPseudoClassState) {
+    return true;
+  }
+
+  // We assume that id and class attributes are used in class/id selectors, and
+  // thus record them.
+  //
+  // TODO(emilio): We keep a filter of the ids in use somewhere in the StyleSet,
+  // presumably we could try to filter the old and new id, but it's not clear
+  // it's worth it.
+  if (aNameSpaceID == kNameSpaceID_None &&
+      (aAttribute == nsGkAtoms::id || aAttribute == nsGkAtoms::_class)) {
+    return true;
+  }
+
+  // We always record lang="", even though we force a subtree restyle when it
+  // changes, since it can change how its siblings match :lang(..) due to
+  // selectors like :lang(..) + div.
+  if (aAttribute == nsGkAtoms::lang) {
+    return true;
+  }
+
+  // Otherwise, just record the attribute change if a selector in the page may
+  // reference it from an attribute selector.
+  return aStyleSet.MightHaveAttributeDependency(aElement, aAttribute);
+}
+
+void RestyleManager::AttributeWillChange(Element* aElement,
+                                         int32_t aNameSpaceID,
+                                         nsAtom* aAttribute, int32_t aModType) {
+  TakeSnapshotForAttributeChange(*aElement, aNameSpaceID, aAttribute);
+}
+
+void RestyleManager::ClassAttributeWillBeChangedBySMIL(Element* aElement) {
+  TakeSnapshotForAttributeChange(*aElement, kNameSpaceID_None,
+                                 nsGkAtoms::_class);
+}
+
+void RestyleManager::TakeSnapshotForAttributeChange(Element& aElement,
+                                                    int32_t aNameSpaceID,
+                                                    nsAtom* aAttribute) {
+  MOZ_DIAGNOSTIC_ASSERT(!mInStyleRefresh);
+
+  bool influencesOtherPseudoClassState;
+  if (!NeedToRecordAttrChange(*StyleSet(), aElement, aNameSpaceID, aAttribute,
+                              &influencesOtherPseudoClassState)) {
+    return;
+  }
+
+  // We cannot tell if the attribute change will affect the styles of
+  // undisplayed elements, because we don't actually restyle those elements
+  // during the restyle traversal. So just assume that the attribute change can
+  // cause the style to change.
+  IncrementUndisplayedRestyleGeneration();
+
+  // Relative selector invalidation travels ancestor and earlier sibling
+  // direction, so it's very possible that it invalidates a styled element.
+  if (!aElement.HasServoData() &&
+      !(aElement.GetSelectorFlags() &
+        NodeSelectorFlags::RelativeSelectorSearchDirectionAncestorSibling)) {
+    return;
+  }
+
+  // Some other random attribute changes may also affect the transitions,
+  // so we also set this true here.
+  mHaveNonAnimationRestyles = true;
+
+  ServoElementSnapshot& snapshot = SnapshotFor(aElement);
+  snapshot.AddAttrs(aElement, aNameSpaceID, aAttribute);
+
+  if (influencesOtherPseudoClassState) {
+    snapshot.AddOtherPseudoClassState(aElement);
+  }
+}
+
+// For some attribute changes we must restyle the whole subtree:
+//
+// * lang="" and xml:lang="" can affect all descendants due to :lang()
+// * exportparts can affect all descendant parts. We could certainly integrate
+//   it better in the invalidation machinery if it was necessary.
+static inline bool AttributeChangeRequiresSubtreeRestyle(
+    const Element& aElement, nsAtom* aAttr) {
+  if (aAttr == nsGkAtoms::exportparts) {
+    // TODO(emilio, bug 1598094): Maybe finer-grained invalidation for
+    // exportparts attribute changes?
+    return !!aElement.GetShadowRoot();
+  }
+  return aAttr == nsGkAtoms::lang;
+}
+
+void RestyleManager::AttributeChanged(Element* aElement, int32_t aNameSpaceID,
+                                      nsAtom* aAttribute, int32_t aModType,
+                                      const nsAttrValue* aOldValue) {
+  MOZ_ASSERT(!mInStyleRefresh);
+
+  auto changeHint = nsChangeHint(0);
+  auto restyleHint = RestyleHint{0};
+
+  changeHint |= aElement->GetAttributeChangeHint(aAttribute, aModType);
+
+  MaybeRestyleForNthOfAttribute(aElement, aAttribute, aOldValue);
+  MaybeRestyleForRelativeSelectorAttribute(aElement, aAttribute, aOldValue);
+
+  if (aAttribute == nsGkAtoms::style) {
+    restyleHint |= RestyleHint::RESTYLE_STYLE_ATTRIBUTE;
+  } else if (AttributeChangeRequiresSubtreeRestyle(*aElement, aAttribute)) {
+    restyleHint |= RestyleHint::RestyleSubtree();
+  } else if (aElement->IsInShadowTree() && aAttribute == nsGkAtoms::part) {
+    // TODO(emilio, bug 1598094): Maybe finer-grained invalidation for part
+    // attribute changes?
+    restyleHint |= RestyleHint::RESTYLE_SELF | RestyleHint::RESTYLE_PSEUDOS;
+  }
+
+  if (nsIFrame* primaryFrame = aElement->GetPrimaryFrame()) {
+    // See if we have appearance information for a theme.
+    StyleAppearance appearance =
+        primaryFrame->StyleDisplay()->EffectiveAppearance();
+    if (appearance != StyleAppearance::None) {
+      nsITheme* theme = PresContext()->Theme();
+      if (theme->ThemeSupportsWidget(PresContext(), primaryFrame, appearance)) {
+        bool repaint = false;
+        theme->WidgetStateChanged(primaryFrame, appearance, aAttribute,
+                                  &repaint, aOldValue);
+        if (repaint) {
+          changeHint |= nsChangeHint_RepaintFrame;
+        }
+      }
+    }
+
+    primaryFrame->AttributeChanged(aNameSpaceID, aAttribute, aModType);
+  }
+
+  if (restyleHint || changeHint) {
+    Servo_NoteExplicitHints(aElement, restyleHint, changeHint);
+  }
+
+  if (restyleHint) {
+    // Assuming we need to invalidate cached style in getComputedStyle for
+    // undisplayed elements, since we don't know if it is needed.
+    IncrementUndisplayedRestyleGeneration();
+
+    // If we change attributes, we have to mark this to be true, so we will
+    // increase the animation generation for the new created transition if any.
+    mHaveNonAnimationRestyles = true;
+  }
+}
+
+void RestyleManager::RestyleSiblingsForNthOf(Element* aChild,
+                                             NodeSelectorFlags aParentFlags) {
+  StyleSet()->RestyleSiblingsForNthOf(*aChild,
+                                      static_cast<uint32_t>(aParentFlags));
+}
+
+void RestyleManager::MaybeRestyleForNthOfAttribute(
+    Element* aChild, nsAtom* aAttribute, const nsAttrValue* aOldValue) {
+  const auto* parentNode = aChild->GetParentNode();
+  MOZ_ASSERT(parentNode);
+  const auto parentFlags = parentNode->GetSelectorFlags();
+  if (!(parentFlags & NodeSelectorFlags::HasSlowSelectorNthOf)) {
+    return;
+  }
+  if (!aChild->HasServoData()) {
+    return;
+  }
+
+  bool mightHaveNthOfDependency;
+  auto& styleSet = *StyleSet();
+  if (aAttribute == nsGkAtoms::id) {
+    auto* const oldAtom = aOldValue->Type() == nsAttrValue::eAtom
+                              ? aOldValue->GetAtomValue()
+                              : nullptr;
+    mightHaveNthOfDependency =
+        styleSet.MightHaveNthOfIDDependency(*aChild, oldAtom, aChild->GetID());
+  } else if (aAttribute == nsGkAtoms::_class) {
+    mightHaveNthOfDependency = styleSet.MightHaveNthOfClassDependency(*aChild);
+  } else {
+    mightHaveNthOfDependency =
+        styleSet.MightHaveNthOfAttributeDependency(*aChild, aAttribute);
+  }
+
+  if (mightHaveNthOfDependency) {
+    RestyleSiblingsForNthOf(aChild, parentFlags);
+  }
+}
+
+void RestyleManager::MaybeRestyleForRelativeSelectorAttribute(
+    Element* aElement, nsAtom* aAttribute, const nsAttrValue* aOldValue) {
+  if (!aElement->HasFlag(ELEMENT_HAS_SNAPSHOT)) {
+    return;
+  }
+  auto& styleSet = *StyleSet();
+  if (aAttribute == nsGkAtoms::id) {
+    auto* const oldAtom = aOldValue->Type() == nsAttrValue::eAtom
+                              ? aOldValue->GetAtomValue()
+                              : nullptr;
+    styleSet.MaybeInvalidateRelativeSelectorIDDependency(
+        *aElement, oldAtom, aElement->GetID(), Snapshots());
+  } else if (aAttribute == nsGkAtoms::_class) {
+    styleSet.MaybeInvalidateRelativeSelectorClassDependency(*aElement,
+                                                            Snapshots());
+  } else {
+    styleSet.MaybeInvalidateRelativeSelectorAttributeDependency(
+        *aElement, aAttribute, Snapshots());
+  }
+}
+
+void RestyleManager::MaybeRestyleForRelativeSelectorState(
+    ServoStyleSet& aStyleSet, Element* aElement, ElementState aChangedBits) {
+  if (!aElement->HasFlag(ELEMENT_HAS_SNAPSHOT)) {
+    return;
+  }
+  aStyleSet.MaybeInvalidateRelativeSelectorStateDependency(
+      *aElement, aChangedBits, Snapshots());
+}
+
+void RestyleManager::ReparentComputedStyleForFirstLine(nsIFrame* aFrame) {
+  // This is only called when moving frames in or out of the first-line
+  // pseudo-element (or one of its descendants).  We can't say much about
+  // aFrame's ancestors, unfortunately (e.g. during a dynamic insert into
+  // something inside an inline-block on the first line the ancestors could be
+  // totally arbitrary), but we will definitely find a line frame on the
+  // ancestor chain.  Note that the lineframe may not actually be the one that
+  // corresponds to ::first-line; when we're moving _out_ of the ::first-line it
+  // will be one of the continuations instead.
+#ifdef DEBUG
+  {
+    nsIFrame* f = aFrame->GetParent();
+    while (f && !f->IsLineFrame()) {
+      f = f->GetParent();
+    }
+    MOZ_ASSERT(f, "Must have found a first-line frame");
+  }
+#endif
+
+  DoReparentComputedStyleForFirstLine(aFrame, *StyleSet());
+}
+
+static bool IsFrameAboutToGoAway(nsIFrame* aFrame) {
+  auto* element = Element::FromNode(aFrame->GetContent());
+  if (!element) {
+    return false;
+  }
+  return !element->HasServoData();
+}
+
+void RestyleManager::DoReparentComputedStyleForFirstLine(
+    nsIFrame* aFrame, ServoStyleSet& aStyleSet) {
+  if (aFrame->IsBackdropFrame()) {
+    // Style context of backdrop frame has no parent style, and thus we do not
+    // need to reparent it.
+    return;
+  }
+
+  if (IsFrameAboutToGoAway(aFrame)) {
+    // We're entering a display: none subtree, which we know it's going to get
+    // rebuilt. Don't bother reparenting.
+    return;
+  }
+
+  if (aFrame->IsPlaceholderFrame()) {
+    // Also reparent the out-of-flow and all its continuations.  We're doing
+    // this to match Gecko for now, but it's not clear that this behavior is
+    // correct per spec.  It's certainly pretty odd for out-of-flows whose
+    // containing block is not within the first line.
+    //
+    // Right now we're somewhat inconsistent in this testcase:
+    //
+    //  <style>
+    //    div { color: orange; clear: left; }
+    //    div::first-line { color: blue; }
+    //  </style>
+    //  <div>
+    //    <span style="float: left">What color is this text?</span>
+    //  </div>
+    //  <div>
+    //    <span><span style="float: left">What color is this text?</span></span>
+    //  </div>
+    //
+    // We make the first float orange and the second float blue.  On the other
+    // hand, if the float were within an inline-block that was on the first
+    // line, arguably it _should_ inherit from the ::first-line...
+    nsIFrame* outOfFlow =
+        nsPlaceholderFrame::GetRealFrameForPlaceholder(aFrame);
+    MOZ_ASSERT(outOfFlow, "no out-of-flow frame");
+    for (; outOfFlow; outOfFlow = outOfFlow->GetNextContinuation()) {
+      DoReparentComputedStyleForFirstLine(outOfFlow, aStyleSet);
+    }
+  }
+
+  // FIXME(emilio): This is the only caller of GetParentComputedStyle, let's try
+  // to remove it?
+  nsIFrame* providerFrame;
+  ComputedStyle* newParentStyle =
+      aFrame->GetParentComputedStyle(&providerFrame);
+  // If our provider is our child, we want to reparent it first, because we
+  // inherit style from it.
+  bool isChild = providerFrame && providerFrame->GetParent() == aFrame;
+  nsIFrame* providerChild = nullptr;
+  if (isChild) {
+    DoReparentComputedStyleForFirstLine(providerFrame, aStyleSet);
+    // Get the style again after ReparentComputedStyle() which might have
+    // changed it.
+    newParentStyle = providerFrame->Style();
+    providerChild = providerFrame;
+    MOZ_ASSERT(!providerFrame->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW),
+               "Out of flow provider?");
+  }
+
+  if (!newParentStyle) {
+    // No need to do anything here for this frame, but we should still reparent
+    // its descendants, because those may have styles that inherit from the
+    // parent of this frame (e.g. non-anonymous columns in an anonymous
+    // colgroup).
+    MOZ_ASSERT(aFrame->Style()->IsNonInheritingAnonBox(),
+               "Why did this frame not end up with a parent context?");
+    ReparentFrameDescendants(aFrame, providerChild, aStyleSet);
+    return;
+  }
+
+  bool isElement = aFrame->GetContent()->IsElement();
+
+  // We probably don't want to initiate transitions from ReparentComputedStyle,
+  // since we call it during frame construction rather than in response to
+  // dynamic changes.
+  // Also see the comment at the start of
+  // nsTransitionManager::ConsiderInitiatingTransition.
+  //
+  // We don't try to do the fancy copying from previous continuations that
+  // GeckoRestyleManager does here, because that relies on knowing the parents
+  // of ComputedStyles, and we don't know those.
+  ComputedStyle* oldStyle = aFrame->Style();
+  Element* ourElement = isElement ? aFrame->GetContent()->AsElement() : nullptr;
+  ComputedStyle* newParent = newParentStyle;
+
+  if (!providerFrame) {
+    // No providerFrame means we inherited from a display:contents thing.  Our
+    // layout parent style is the style of our nearest ancestor frame.  But we
+    // have to be careful to do that with our placeholder, not with us, if we're
+    // out of flow.
+    if (aFrame->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW)) {
+      aFrame->FirstContinuation()
+          ->GetPlaceholderFrame()
+          ->GetLayoutParentStyleForOutOfFlow(&providerFrame);
+    } else {
+      providerFrame = nsIFrame::CorrectStyleParentFrame(
+          aFrame->GetParent(), oldStyle->GetPseudoType());
+    }
+  }
+  ComputedStyle* layoutParent = providerFrame->Style();
+
+  RefPtr<ComputedStyle> newStyle = aStyleSet.ReparentComputedStyle(
+      oldStyle, newParent, layoutParent, ourElement);
+  aFrame->SetComputedStyle(newStyle);
+
+  // This logic somewhat mirrors the logic in
+  // RestyleManager::ProcessPostTraversal.
+  if (isElement) {
+    // We can't use UpdateAdditionalComputedStyles as-is because it needs a
+    // ServoRestyleState and maintaining one of those during a _frametree_
+    // traversal is basically impossible.
+    int32_t index = 0;
+    while (auto* oldAdditionalStyle =
+               aFrame->GetAdditionalComputedStyle(index)) {
+      RefPtr<ComputedStyle> newAdditionalContext =
+          aStyleSet.ReparentComputedStyle(oldAdditionalStyle, newStyle,
+                                          newStyle, nullptr);
+      aFrame->SetAdditionalComputedStyle(index, newAdditionalContext);
+      ++index;
+    }
+  }
+
+  // Generally, owned anon boxes are our descendants.  The only exceptions are
+  // tables (for the table wrapper) and inline frames (for the block part of the
+  // block-in-inline split).  We're going to update our descendants when looping
+  // over kids, and we don't want to update the block part of a block-in-inline
+  // split if the inline is on the first line but the block is not (and if the
+  // block is, it's the child of something else on the first line and will get
+  // updated as a child).  And given how this method ends up getting called, if
+  // we reach here for a table frame, we are already in the middle of
+  // reparenting the table wrapper frame.  So no need to
+  // UpdateStyleOfOwnedAnonBoxes() here.
+
+  ReparentFrameDescendants(aFrame, providerChild, aStyleSet);
+
+  // We do not need to do the equivalent of UpdateFramePseudoElementStyles,
+  // because those are handled by our descendant walk.
+}
+
+void RestyleManager::ReparentFrameDescendants(nsIFrame* aFrame,
+                                              nsIFrame* aProviderChild,
+                                              ServoStyleSet& aStyleSet) {
+  for (const auto& childList : aFrame->ChildLists()) {
+    for (nsIFrame* child : childList.mList) {
+      // only do frames that are in flow
+      if (!child->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW) &&
+          child != aProviderChild) {
+        DoReparentComputedStyleForFirstLine(child, aStyleSet);
+      }
+    }
+  }
+}
+
+}  // namespace mozilla