From 36d22d82aa202bb199967e9512281e9a53db42c9 Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Sun, 7 Apr 2024 21:33:14 +0200
Subject: Adding upstream version 115.7.0esr.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 dom/base/ResizeObserver.cpp | 604 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 604 insertions(+)
 create mode 100644 dom/base/ResizeObserver.cpp

(limited to 'dom/base/ResizeObserver.cpp')

diff --git a/dom/base/ResizeObserver.cpp b/dom/base/ResizeObserver.cpp
new file mode 100644
index 0000000000..cc9865ee2e
--- /dev/null
+++ b/dom/base/ResizeObserver.cpp
@@ -0,0 +1,604 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* 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/dom/ResizeObserver.h"
+
+#include "mozilla/dom/DOMRect.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/SVGUtils.h"
+#include "nsIContent.h"
+#include "nsIContentInlines.h"
+#include "nsIScrollableFrame.h"
+#include "nsLayoutUtils.h"
+#include <limits>
+
+namespace mozilla::dom {
+
+/**
+ * Returns the length of the parent-traversal path (in terms of the number of
+ * nodes) to an unparented/root node from aNode. An unparented/root node is
+ * considered to have a depth of 1, its children have a depth of 2, etc.
+ * aNode is expected to be non-null.
+ * Note: The shadow root is not part of the calculation because the caller,
+ * ResizeObserver, doesn't observe the shadow root, and only needs relative
+ * depths among all the observed targets. In other words, we calculate the
+ * depth of the flattened tree.
+ *
+ * However, these is a spec issue about how to handle shadow DOM case. We
+ * may need to update this function later:
+ *   https://github.com/w3c/csswg-drafts/issues/3840
+ *
+ * https://drafts.csswg.org/resize-observer/#calculate-depth-for-node-h
+ */
+static uint32_t GetNodeDepth(nsINode* aNode) {
+  uint32_t depth = 1;
+
+  MOZ_ASSERT(aNode, "Node shouldn't be null");
+
+  // Use GetFlattenedTreeParentNode to bypass the shadow root and cross the
+  // shadow boundary to calculate the node depth without the shadow root.
+  while ((aNode = aNode->GetFlattenedTreeParentNode())) {
+    ++depth;
+  }
+
+  return depth;
+}
+
+static nsSize GetContentRectSize(const nsIFrame& aFrame) {
+  if (const nsIScrollableFrame* f = do_QueryFrame(&aFrame)) {
+    // We return the scrollport rect for compat with other UAs, see bug 1733042.
+    // But the scrollPort includes padding (but not border!), so remove it.
+    nsRect scrollPort = f->GetScrollPortRect();
+    nsMargin padding =
+        aFrame.GetUsedPadding().ApplySkipSides(aFrame.GetSkipSides());
+    scrollPort.Deflate(padding);
+    // This can break in some edge cases like when layout overflows sizes or
+    // what not.
+    NS_ASSERTION(
+        !aFrame.PresContext()->UseOverlayScrollbars() ||
+            scrollPort.Size() == aFrame.GetContentRectRelativeToSelf().Size(),
+        "Wrong scrollport?");
+    return scrollPort.Size();
+  }
+  return aFrame.GetContentRectRelativeToSelf().Size();
+}
+
+/**
+ * Returns |aTarget|'s size in the form of gfx::Size (in pixels).
+ * If the target is an SVG that does not participate in CSS layout,
+ * its width and height are determined from bounding box.
+ *
+ * https://www.w3.org/TR/resize-observer-1/#calculate-box-size
+ */
+static AutoTArray<LogicalPixelSize, 1> CalculateBoxSize(
+    Element* aTarget, ResizeObserverBoxOptions aBox,
+    const ResizeObserver& aObserver) {
+  nsIFrame* frame = aTarget->GetPrimaryFrame();
+
+  if (!frame) {
+    // TODO: Should this return an empty array instead?
+    // https://github.com/w3c/csswg-drafts/issues/7734
+    return {LogicalPixelSize()};
+  }
+
+  if (frame->HasAnyStateBits(NS_FRAME_SVG_LAYOUT)) {
+    // Per the spec, this target's SVG size is always its bounding box size no
+    // matter what box option you choose, because SVG elements do not use
+    // standard CSS box model.
+    // TODO: what if the SVG is fragmented?
+    // https://github.com/w3c/csswg-drafts/issues/7736
+    const gfxRect bbox = SVGUtils::GetBBox(frame);
+    gfx::Size size(static_cast<float>(bbox.width),
+                   static_cast<float>(bbox.height));
+    const WritingMode wm = frame->GetWritingMode();
+    if (aBox == ResizeObserverBoxOptions::Device_pixel_content_box) {
+      // Per spec, we calculate the inline/block sizes to target’s bounding box
+      // {inline|block} length, in integral device pixels, so we round the final
+      // result.
+      // https://drafts.csswg.org/resize-observer/#dom-resizeobserverboxoptions-device-pixel-content-box
+      const LayoutDeviceIntSize snappedSize =
+          RoundedToInt(CSSSize::FromUnknownSize(size) *
+                       frame->PresContext()->CSSToDevPixelScale());
+      return {LogicalPixelSize(wm, gfx::Size(snappedSize.ToUnknownSize()))};
+    }
+    return {LogicalPixelSize(wm, size)};
+  }
+
+  // Per the spec, non-replaced inline Elements will always have an empty
+  // content rect. Therefore, we always use the same trivially-empty size
+  // for non-replaced inline elements here, and their IsActive() will
+  // always return false. (So its observation won't be fired.)
+  // TODO: Should we use an empty array instead?
+  // https://github.com/w3c/csswg-drafts/issues/7734
+  if (!frame->IsFrameOfType(nsIFrame::eReplaced) &&
+      frame->IsFrameOfType(nsIFrame::eLineParticipant)) {
+    return {LogicalPixelSize()};
+  }
+
+  auto GetFrameSize = [aBox](nsIFrame* aFrame) {
+    switch (aBox) {
+      case ResizeObserverBoxOptions::Border_box:
+        return CSSPixel::FromAppUnits(aFrame->GetSize()).ToUnknownSize();
+      case ResizeObserverBoxOptions::Device_pixel_content_box: {
+        // Simply converting from app units to device units is insufficient - we
+        // need to take subpixel snapping into account. Subpixel snapping
+        // happens with respect to the reference frame, so do the dev pixel
+        // conversion with our rectangle positioned relative to the reference
+        // frame, then get the size from there.
+        const auto* referenceFrame = nsLayoutUtils::GetReferenceFrame(aFrame);
+        // GetOffsetToCrossDoc version handles <iframe>s in addition to normal
+        // cases. We don't expect this to tight loop for additional checks to
+        // matter.
+        const auto offset = aFrame->GetOffsetToCrossDoc(referenceFrame);
+        const auto contentSize = GetContentRectSize(*aFrame);
+        // Casting to double here is deliberate to minimize rounding error in
+        // upcoming operations.
+        const auto appUnitsPerDevPixel =
+            static_cast<double>(aFrame->PresContext()->AppUnitsPerDevPixel());
+        // Calculation here is a greatly simplified version of
+        // `NSRectToSnappedRect` as 1) we're not actually drawing (i.e. no draw
+        // target), and 2) transform does not need to be taken into account.
+        gfx::Rect rect{gfx::Float(offset.X() / appUnitsPerDevPixel),
+                       gfx::Float(offset.Y() / appUnitsPerDevPixel),
+                       gfx::Float(contentSize.Width() / appUnitsPerDevPixel),
+                       gfx::Float(contentSize.Height() / appUnitsPerDevPixel)};
+        gfx::Point tl = rect.TopLeft().Round();
+        gfx::Point br = rect.BottomRight().Round();
+
+        rect.SizeTo(gfx::Size(br.x - tl.x, br.y - tl.y));
+        rect.NudgeToIntegers();
+        return rect.Size().ToUnknownSize();
+      }
+      case ResizeObserverBoxOptions::Content_box:
+      default:
+        break;
+    }
+    return CSSPixel::FromAppUnits(GetContentRectSize(*aFrame)).ToUnknownSize();
+  };
+  if (!StaticPrefs::dom_resize_observer_support_fragments() &&
+      !aObserver.HasNativeCallback()) {
+    return {LogicalPixelSize(frame->GetWritingMode(), GetFrameSize(frame))};
+  }
+  AutoTArray<LogicalPixelSize, 1> size;
+  for (nsIFrame* cur = frame; cur; cur = cur->GetNextContinuation()) {
+    const WritingMode wm = cur->GetWritingMode();
+    size.AppendElement(LogicalPixelSize(wm, GetFrameSize(cur)));
+  }
+  return size;
+}
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(ResizeObservation)
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(ResizeObservation)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mTarget);
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(ResizeObservation)
+  tmp->Unlink(RemoveFromObserver::Yes);
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+ResizeObservation::ResizeObservation(Element& aTarget,
+                                     ResizeObserver& aObserver,
+                                     ResizeObserverBoxOptions aBox)
+    : mTarget(&aTarget),
+      mObserver(&aObserver),
+      mObservedBox(aBox),
+      mLastReportedSize(
+          {StaticPrefs::dom_resize_observer_last_reported_size_invalid()
+               ? LogicalPixelSize(WritingMode(), gfx::Size(-1, -1))
+               : LogicalPixelSize()}) {
+  aTarget.BindObject(mObserver);
+}
+
+void ResizeObservation::Unlink(RemoveFromObserver aRemoveFromObserver) {
+  ResizeObserver* observer = std::exchange(mObserver, nullptr);
+  nsCOMPtr<Element> target = std::move(mTarget);
+  if (observer && target) {
+    if (aRemoveFromObserver == RemoveFromObserver::Yes) {
+      observer->Unobserve(*target);
+    }
+    target->UnbindObject(observer);
+  }
+}
+
+bool ResizeObservation::IsActive() const {
+  // As detailed in the css-contain specification, if the target is hidden by
+  // `content-visibility` it should not call its ResizeObservation callbacks.
+  nsIFrame* frame = mTarget->GetPrimaryFrame();
+  if (frame && frame->IsHiddenByContentVisibilityOnAnyAncestor()) {
+    return false;
+  }
+
+  return mLastReportedSize !=
+         CalculateBoxSize(mTarget, mObservedBox, *mObserver);
+}
+
+void ResizeObservation::UpdateLastReportedSize(
+    const nsTArray<LogicalPixelSize>& aSize) {
+  mLastReportedSize.Assign(aSize);
+}
+
+// Only needed for refcounted objects.
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(ResizeObserver)
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(ResizeObserver)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mOwner, mDocument, mActiveTargets,
+                                    mObservationMap);
+  if (tmp->mCallback.is<RefPtr<ResizeObserverCallback>>()) {
+    ImplCycleCollectionTraverse(
+        cb, tmp->mCallback.as<RefPtr<ResizeObserverCallback>>(), "mCallback",
+        0);
+  }
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(ResizeObserver)
+  tmp->Disconnect();
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mOwner, mDocument, mActiveTargets,
+                                  mObservationMap);
+  if (tmp->mCallback.is<RefPtr<ResizeObserverCallback>>()) {
+    ImplCycleCollectionUnlink(
+        tmp->mCallback.as<RefPtr<ResizeObserverCallback>>());
+  }
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(ResizeObserver)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(ResizeObserver)
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(ResizeObserver)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+ResizeObserver::ResizeObserver(Document& aDocument, NativeCallback aCallback)
+    : mOwner(aDocument.GetInnerWindow()),
+      mDocument(&aDocument),
+      mCallback(aCallback) {
+  MOZ_ASSERT(mOwner, "Need a non-null owner window");
+  MOZ_ASSERT(mDocument == mOwner->GetExtantDoc());
+}
+
+already_AddRefed<ResizeObserver> ResizeObserver::Constructor(
+    const GlobalObject& aGlobal, ResizeObserverCallback& aCb,
+    ErrorResult& aRv) {
+  nsCOMPtr<nsPIDOMWindowInner> window =
+      do_QueryInterface(aGlobal.GetAsSupports());
+  if (!window) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+
+  Document* doc = window->GetExtantDoc();
+  if (!doc) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+
+  return do_AddRef(new ResizeObserver(std::move(window), doc, aCb));
+}
+
+void ResizeObserver::Observe(Element& aTarget,
+                             const ResizeObserverOptions& aOptions) {
+  if (MOZ_UNLIKELY(!mDocument)) {
+    MOZ_ASSERT_UNREACHABLE("How did we call observe() after unlink?");
+    return;
+  }
+
+  // NOTE(emilio): Per spec, this is supposed to happen on construction, but the
+  // spec isn't particularly sane here, see
+  // https://github.com/w3c/csswg-drafts/issues/4518
+  if (mObservationList.isEmpty()) {
+    MOZ_ASSERT(mObservationMap.IsEmpty());
+    mDocument->AddResizeObserver(*this);
+  }
+
+  auto& observation = mObservationMap.LookupOrInsert(&aTarget);
+  if (observation) {
+    if (observation->BoxOptions() == aOptions.mBox) {
+      // Already observed this target and the observed box is the same, so
+      // return.
+      // Note: Based on the spec, we should unobserve it first. However,
+      // calling Unobserve() when we observe the same box will remove original
+      // ResizeObservation and then add a new one, this may cause an unexpected
+      // result because ResizeObservation stores the mLastReportedSize which
+      // should be kept to make sure IsActive() returns the correct result.
+      return;
+    }
+    // Remove the pre-existing entry, but without unregistering ourselves from
+    // the controller.
+    observation->remove();
+    observation = nullptr;
+  }
+
+  observation = new ResizeObservation(aTarget, *this, aOptions.mBox);
+  if (!StaticPrefs::dom_resize_observer_last_reported_size_invalid() &&
+      this == mDocument->GetLastRememberedSizeObserver()) {
+    // Resize observations are initialized with a (0, 0) mLastReportedSize,
+    // this means that the callback won't be called if the element is 0x0.
+    // But we need it called for handling the last remembered size, so set
+    // mLastReportedSize to an invalid size to ensure IsActive() is true
+    // for the current element size.
+    // See https://github.com/w3c/csswg-drafts/issues/3664 about doing this in
+    // the general case, then we won't need this hack for the last remembered
+    // size, and will have consistency with IntersectionObserver.
+    observation->UpdateLastReportedSize(
+        {LogicalPixelSize(WritingMode(), gfx::Size(-1, -1))});
+    MOZ_ASSERT(observation->IsActive());
+  }
+  mObservationList.insertBack(observation);
+
+  // Per the spec, we need to trigger notification in event loop that
+  // contains ResizeObserver observe call even when resize/reflow does
+  // not happen.
+  mDocument->ScheduleResizeObserversNotification();
+}
+
+void ResizeObserver::Unobserve(Element& aTarget) {
+  RefPtr<ResizeObservation> observation;
+  if (!mObservationMap.Remove(&aTarget, getter_AddRefs(observation))) {
+    return;
+  }
+
+  MOZ_ASSERT(!mObservationList.isEmpty(),
+             "If ResizeObservation found for an element, observation list "
+             "must be not empty.");
+  observation->remove();
+  if (mObservationList.isEmpty()) {
+    if (MOZ_LIKELY(mDocument)) {
+      mDocument->RemoveResizeObserver(*this);
+    }
+  }
+}
+
+void ResizeObserver::Disconnect() {
+  const bool registered = !mObservationList.isEmpty();
+  while (auto* observation = mObservationList.popFirst()) {
+    observation->Unlink(ResizeObservation::RemoveFromObserver::No);
+  }
+  MOZ_ASSERT(mObservationList.isEmpty());
+  mObservationMap.Clear();
+  mActiveTargets.Clear();
+  if (registered && MOZ_LIKELY(mDocument)) {
+    mDocument->RemoveResizeObserver(*this);
+  }
+}
+
+void ResizeObserver::GatherActiveObservations(uint32_t aDepth) {
+  mActiveTargets.Clear();
+  mHasSkippedTargets = false;
+
+  for (auto* observation : mObservationList) {
+    if (!observation->IsActive()) {
+      continue;
+    }
+
+    uint32_t targetDepth = GetNodeDepth(observation->Target());
+
+    if (targetDepth > aDepth) {
+      mActiveTargets.AppendElement(observation);
+    } else {
+      mHasSkippedTargets = true;
+    }
+  }
+}
+
+uint32_t ResizeObserver::BroadcastActiveObservations() {
+  uint32_t shallowestTargetDepth = std::numeric_limits<uint32_t>::max();
+
+  if (!HasActiveObservations()) {
+    return shallowestTargetDepth;
+  }
+
+  Sequence<OwningNonNull<ResizeObserverEntry>> entries;
+
+  for (auto& observation : mActiveTargets) {
+    Element* target = observation->Target();
+
+    auto borderBoxSize =
+        CalculateBoxSize(target, ResizeObserverBoxOptions::Border_box, *this);
+    auto contentBoxSize =
+        CalculateBoxSize(target, ResizeObserverBoxOptions::Content_box, *this);
+    auto devicePixelContentBoxSize = CalculateBoxSize(
+        target, ResizeObserverBoxOptions::Device_pixel_content_box, *this);
+    RefPtr<ResizeObserverEntry> entry =
+        new ResizeObserverEntry(mOwner, *target, borderBoxSize, contentBoxSize,
+                                devicePixelContentBoxSize);
+
+    if (!entries.AppendElement(entry.forget(), fallible)) {
+      // Out of memory.
+      break;
+    }
+
+    // Sync the broadcast size of observation so the next size inspection
+    // will be based on the updated size from last delivered observations.
+    switch (observation->BoxOptions()) {
+      case ResizeObserverBoxOptions::Border_box:
+        observation->UpdateLastReportedSize(borderBoxSize);
+        break;
+      case ResizeObserverBoxOptions::Device_pixel_content_box:
+        observation->UpdateLastReportedSize(devicePixelContentBoxSize);
+        break;
+      case ResizeObserverBoxOptions::Content_box:
+      default:
+        observation->UpdateLastReportedSize(contentBoxSize);
+    }
+
+    uint32_t targetDepth = GetNodeDepth(observation->Target());
+
+    if (targetDepth < shallowestTargetDepth) {
+      shallowestTargetDepth = targetDepth;
+    }
+  }
+
+  if (mCallback.is<RefPtr<ResizeObserverCallback>>()) {
+    RefPtr<ResizeObserverCallback> callback(
+        mCallback.as<RefPtr<ResizeObserverCallback>>());
+    callback->Call(this, entries, *this);
+  } else {
+    mCallback.as<NativeCallback>()(entries, *this);
+  }
+
+  mActiveTargets.Clear();
+  mHasSkippedTargets = false;
+
+  return shallowestTargetDepth;
+}
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(ResizeObserverEntry, mOwner, mTarget,
+                                      mContentRect, mBorderBoxSize,
+                                      mContentBoxSize,
+                                      mDevicePixelContentBoxSize)
+NS_IMPL_CYCLE_COLLECTING_ADDREF(ResizeObserverEntry)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(ResizeObserverEntry)
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(ResizeObserverEntry)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+void ResizeObserverEntry::GetBorderBoxSize(
+    nsTArray<RefPtr<ResizeObserverSize>>& aRetVal) const {
+  // In the resize-observer-1 spec, there will only be a single
+  // ResizeObserverSize returned in the FrozenArray for now.
+  //
+  // Note: the usage of FrozenArray is to support elements that have multiple
+  // fragments, which occur in multi-column scenarios.
+  // https://drafts.csswg.org/resize-observer/#resize-observer-entry-interface
+  aRetVal.Assign(mBorderBoxSize);
+}
+
+void ResizeObserverEntry::GetContentBoxSize(
+    nsTArray<RefPtr<ResizeObserverSize>>& aRetVal) const {
+  // In the resize-observer-1 spec, there will only be a single
+  // ResizeObserverSize returned in the FrozenArray for now.
+  //
+  // Note: the usage of FrozenArray is to support elements that have multiple
+  // fragments, which occur in multi-column scenarios.
+  // https://drafts.csswg.org/resize-observer/#resize-observer-entry-interface
+  aRetVal.Assign(mContentBoxSize);
+}
+
+void ResizeObserverEntry::GetDevicePixelContentBoxSize(
+    nsTArray<RefPtr<ResizeObserverSize>>& aRetVal) const {
+  // In the resize-observer-1 spec, there will only be a single
+  // ResizeObserverSize returned in the FrozenArray for now.
+  //
+  // Note: the usage of FrozenArray is to support elements that have multiple
+  // fragments, which occur in multi-column scenarios.
+  // https://drafts.csswg.org/resize-observer/#resize-observer-entry-interface
+  aRetVal.Assign(mDevicePixelContentBoxSize);
+}
+
+void ResizeObserverEntry::SetBorderBoxSize(
+    const nsTArray<LogicalPixelSize>& aSize) {
+  mBorderBoxSize.Clear();
+  mBorderBoxSize.SetCapacity(aSize.Length());
+  for (const LogicalPixelSize& size : aSize) {
+    mBorderBoxSize.AppendElement(new ResizeObserverSize(mOwner, size));
+  }
+}
+
+void ResizeObserverEntry::SetContentRectAndSize(
+    const nsTArray<LogicalPixelSize>& aSize) {
+  nsIFrame* frame = mTarget->GetPrimaryFrame();
+
+  // 1. Update mContentRect.
+  nsMargin padding = frame ? frame->GetUsedPadding() : nsMargin();
+  // Per the spec, we need to use the top-left padding offset as the origin of
+  // our contentRect.
+  gfx::Size sizeForRect;
+  MOZ_DIAGNOSTIC_ASSERT(!aSize.IsEmpty());
+  if (!aSize.IsEmpty()) {
+    const WritingMode wm = frame ? frame->GetWritingMode() : WritingMode();
+    sizeForRect = aSize[0].PhysicalSize(wm);
+  }
+  nsRect rect(nsPoint(padding.left, padding.top),
+              CSSPixel::ToAppUnits(CSSSize::FromUnknownSize(sizeForRect)));
+  RefPtr<DOMRect> contentRect = new DOMRect(mOwner);
+  contentRect->SetLayoutRect(rect);
+  mContentRect = std::move(contentRect);
+
+  // 2. Update mContentBoxSize.
+  mContentBoxSize.Clear();
+  mContentBoxSize.SetCapacity(aSize.Length());
+  for (const LogicalPixelSize& size : aSize) {
+    mContentBoxSize.AppendElement(new ResizeObserverSize(mOwner, size));
+  }
+}
+
+void ResizeObserverEntry::SetDevicePixelContentSize(
+    const nsTArray<LogicalPixelSize>& aSize) {
+  mDevicePixelContentBoxSize.Clear();
+  mDevicePixelContentBoxSize.SetCapacity(aSize.Length());
+  for (const LogicalPixelSize& size : aSize) {
+    mDevicePixelContentBoxSize.AppendElement(
+        new ResizeObserverSize(mOwner, size));
+  }
+}
+
+static void LastRememberedSizeCallback(
+    const Sequence<OwningNonNull<ResizeObserverEntry>>& aEntries,
+    ResizeObserver& aObserver) {
+  for (const auto& entry : aEntries) {
+    Element* target = entry->Target();
+    if (!target->IsInComposedDoc()) {
+      aObserver.Unobserve(*target);
+      target->RemoveLastRememberedBSize();
+      target->RemoveLastRememberedISize();
+      continue;
+    }
+    nsIFrame* frame = target->GetPrimaryFrame();
+    if (!frame) {
+      aObserver.Unobserve(*target);
+      continue;
+    }
+    MOZ_ASSERT(!frame->IsFrameOfType(nsIFrame::eLineParticipant) ||
+                   frame->IsFrameOfType(nsIFrame::eReplaced),
+               "Should have unobserved non-replaced inline.");
+    MOZ_ASSERT(!frame->HidesContent(),
+               "Should have unobserved element skipping its contents.");
+    const nsStylePosition* stylePos = frame->StylePosition();
+    const WritingMode wm = frame->GetWritingMode();
+    bool canUpdateBSize = stylePos->ContainIntrinsicBSize(wm).IsAutoLength();
+    bool canUpdateISize = stylePos->ContainIntrinsicISize(wm).IsAutoLength();
+    MOZ_ASSERT(canUpdateBSize || !target->HasLastRememberedBSize(),
+               "Should have removed the last remembered block size.");
+    MOZ_ASSERT(canUpdateISize || !target->HasLastRememberedISize(),
+               "Should have removed the last remembered inline size.");
+    MOZ_ASSERT(canUpdateBSize || canUpdateISize,
+               "Should have unobserved if we can't update any size.");
+    AutoTArray<RefPtr<ResizeObserverSize>, 1> contentSizeList;
+    entry->GetContentBoxSize(contentSizeList);
+    MOZ_ASSERT(!contentSizeList.IsEmpty());
+    if (canUpdateBSize) {
+      float bSize = 0;
+      for (const auto& current : contentSizeList) {
+        bSize += current->BlockSize();
+      }
+      target->SetLastRememberedBSize(bSize);
+    }
+    if (canUpdateISize) {
+      float iSize = 0;
+      for (const auto& current : contentSizeList) {
+        iSize = std::max(iSize, current->InlineSize());
+      }
+      target->SetLastRememberedISize(iSize);
+    }
+  }
+}
+
+/* static */ already_AddRefed<ResizeObserver>
+ResizeObserver::CreateLastRememberedSizeObserver(Document& aDocument) {
+  return do_AddRef(new ResizeObserver(aDocument, LastRememberedSizeCallback));
+}
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(ResizeObserverSize, mOwner)
+NS_IMPL_CYCLE_COLLECTING_ADDREF(ResizeObserverSize)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(ResizeObserverSize)
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(ResizeObserverSize)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+}  // namespace mozilla::dom
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