Adding upstream version 86.0.1.upstream/86.0.1upstream

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

1 files changed, 1736 insertions, 0 deletions

diff --git a/layout/generic/nsGfxScrollFrame.h b/layout/generic/nsGfxScrollFrame.h
new file mode 100644
index 0000000000..0374244d65
--- /dev/null
+++ b/layout/generic/nsGfxScrollFrame.h
@@ -0,0 +1,1736 @@
+/* -*- 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/. */
+
+/* rendering object to wrap rendering objects that should be scrollable */
+
+#ifndef nsGfxScrollFrame_h___
+#define nsGfxScrollFrame_h___
+
+#include "mozilla/Attributes.h"
+#include "nsContainerFrame.h"
+#include "nsIAnonymousContentCreator.h"
+#include "nsBoxFrame.h"
+#include "nsIScrollableFrame.h"
+#include "nsIScrollbarMediator.h"
+#include "nsIStatefulFrame.h"
+#include "nsThreadUtils.h"
+#include "nsIReflowCallback.h"
+#include "nsBoxLayoutState.h"
+#include "nsQueryFrame.h"
+#include "nsExpirationTracker.h"
+#include "TextOverflow.h"
+#include "ScrollVelocityQueue.h"
+#include "mozilla/ScrollTypes.h"
+#include "mozilla/PresState.h"
+#include "mozilla/layout/ScrollAnchorContainer.h"
+
+class nsPresContext;
+class nsIContent;
+class nsAtom;
+class nsIScrollPositionListener;
+
+namespace mozilla {
+class PresShell;
+struct ScrollReflowInput;
+namespace layers {
+class Layer;
+class LayerManager;
+}  // namespace layers
+namespace layout {
+class ScrollbarActivity;
+}  // namespace layout
+
+class ScrollFrameHelper : public nsIReflowCallback {
+ public:
+  typedef nsIFrame::Sides Sides;
+  typedef mozilla::CSSIntPoint CSSIntPoint;
+  typedef mozilla::layout::ScrollbarActivity ScrollbarActivity;
+  typedef mozilla::layers::FrameMetrics FrameMetrics;
+  typedef mozilla::layers::ScrollableLayerGuid ScrollableLayerGuid;
+  typedef mozilla::layers::ScrollSnapInfo ScrollSnapInfo;
+  typedef mozilla::layers::Layer Layer;
+  typedef mozilla::layers::LayerManager LayerManager;
+  typedef mozilla::layout::ScrollAnchorContainer ScrollAnchorContainer;
+  using Element = mozilla::dom::Element;
+
+  class AsyncScroll;
+  class AsyncSmoothMSDScroll;
+
+  ScrollFrameHelper(nsContainerFrame* aOuter, bool aIsRoot);
+  ~ScrollFrameHelper();
+
+  mozilla::ScrollStyles GetScrollStylesFromFrame() const;
+  mozilla::layers::OverscrollBehaviorInfo GetOverscrollBehaviorInfo() const;
+
+  bool IsForTextControlWithNoScrollbars() const;
+
+  // If a child frame was added or removed on the scrollframe,
+  // reload our child frame list.
+  // We need this if a scrollbar frame is recreated.
+  void ReloadChildFrames();
+
+  nsresult CreateAnonymousContent(
+      nsTArray<nsIAnonymousContentCreator::ContentInfo>& aElements);
+  void AppendAnonymousContentTo(nsTArray<nsIContent*>& aElements,
+                                uint32_t aFilter);
+  nsresult FireScrollPortEvent();
+  void PostScrollEndEvent();
+  void FireScrollEndEvent();
+  void PostOverflowEvent();
+  using PostDestroyData = nsIFrame::PostDestroyData;
+  void Destroy(PostDestroyData& aPostDestroyData);
+
+  void BuildDisplayList(nsDisplayListBuilder* aBuilder,
+                        const nsDisplayListSet& aLists);
+
+  // Add display items for the top-layer (which includes things like
+  // the fullscreen element, its backdrop, and text selection carets)
+  // to |aLists|.
+  // This is a no-op for scroll frames other than the viewport's
+  // root scroll frame.
+  // This should be called with an nsDisplayListSet that will be
+  // wrapped in the async zoom container, if we're building one.
+  // It should not be called with an ASR setter on the stack, as the
+  // top-layer items handle setting up their own ASRs.
+  nsDisplayWrapList* MaybeCreateTopLayerItems(nsDisplayListBuilder* aBuilder,
+                                              bool* aIsOpaque);
+
+  void AppendScrollPartsTo(nsDisplayListBuilder* aBuilder,
+                           const nsDisplayListSet& aLists, bool aCreateLayer,
+                           bool aPositioned);
+
+  bool GetBorderRadii(const nsSize& aFrameSize, const nsSize& aBorderArea,
+                      Sides aSkipSides, nscoord aRadii[8]) const;
+
+  // nsIReflowCallback
+  bool ReflowFinished() final;
+  void ReflowCallbackCanceled() final;
+
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   * Called when the 'curpos' attribute on one of the scrollbars changes.
+   */
+  void CurPosAttributeChanged(nsIContent* aChild, bool aDoScroll = true);
+
+  void PostScrollEvent(bool aDelayed = false);
+  void FireScrollEvent();
+  void PostScrolledAreaEvent();
+  void FireScrolledAreaEvent();
+
+  bool IsSmoothScrollingEnabled();
+
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void FinishReflowForScrollbar(Element* aElement, nscoord aMinXY,
+                                nscoord aMaxXY, nscoord aCurPosXY,
+                                nscoord aPageIncrement, nscoord aIncrement);
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void SetScrollbarEnabled(Element* aElement, nscoord aMaxPos);
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void SetCoordAttribute(Element* aElement, nsAtom* aAtom, nscoord aSize);
+
+  nscoord GetCoordAttribute(nsIFrame* aFrame, nsAtom* aAtom,
+                            nscoord aDefaultValue, nscoord* aRangeStart,
+                            nscoord* aRangeLength);
+
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   * Update scrollbar curpos attributes to reflect current scroll position
+   */
+  void UpdateScrollbarPosition();
+
+  nsSize GetLayoutSize() const {
+    if (mIsUsingMinimumScaleSize) {
+      return mICBSize;
+    }
+    return mScrollPort.Size();
+  }
+  nsRect GetScrollPortRect() const { return mScrollPort; }
+  nsPoint GetScrollPosition() const {
+    return mScrollPort.TopLeft() - mScrolledFrame->GetPosition();
+  }
+  /**
+   * For LTR frames, the logical scroll position is the offset of the top left
+   * corner of the frame from the top left corner of the scroll port (same as
+   * GetScrollPosition).
+   * For RTL frames, it is the offset of the top right corner of the frame from
+   * the top right corner of the scroll port
+   */
+  nsPoint GetLogicalScrollPosition() const {
+    nsPoint pt;
+    pt.x = IsPhysicalLTR()
+               ? mScrollPort.x - mScrolledFrame->GetPosition().x
+               : mScrollPort.XMost() - mScrolledFrame->GetRect().XMost();
+    pt.y = mScrollPort.y - mScrolledFrame->GetPosition().y;
+    return pt;
+  }
+  nsRect GetLayoutScrollRange() const;
+  // Get the scroll range assuming the viewport has size (aWidth, aHeight).
+  nsRect GetScrollRange(nscoord aWidth, nscoord aHeight) const;
+  nsSize GetVisualViewportSize() const;
+  nsPoint GetVisualViewportOffset() const;
+  bool SetVisualViewportOffset(const nsPoint& aOffset, bool aRepaint);
+  nsRect GetVisualScrollRange() const;
+  nsRect GetScrollRangeForUserInputEvents() const;
+
+  /**
+   * Return the 'optimal viewing region' as a rect suitable for use by
+   * scroll anchoring. This rect is in the same coordinate space as
+   * 'GetScrollPortRect', and accounts for 'scroll-padding' as defined by:
+   *
+   * https://drafts.csswg.org/css-scroll-snap-1/#optimal-viewing-region
+   */
+  nsRect GetVisualOptimalViewingRect() const;
+
+  /**
+   * For LTR frames, this is the same as GetVisualViewportOffset().
+   * For RTL frames, we take the offset from the top right corner of the frame
+   * to the top right corner of the visual viewport.
+   */
+  nsPoint GetLogicalVisualViewportOffset() const {
+    nsPoint pt = GetVisualViewportOffset();
+    if (!IsPhysicalLTR()) {
+      pt.x += GetVisualViewportSize().width - mScrolledFrame->GetRect().width;
+    }
+    return pt;
+  }
+  void ScrollSnap(ScrollMode aMode = ScrollMode::SmoothMsd);
+  void ScrollSnap(const nsPoint& aDestination,
+                  ScrollMode aMode = ScrollMode::SmoothMsd);
+
+  bool HasPendingScrollRestoration() const {
+    return mRestorePos != nsPoint(-1, -1);
+  }
+
+  bool IsProcessingScrollEvent() const { return mProcessingScrollEvent; }
+
+ public:
+  static void AsyncScrollCallback(ScrollFrameHelper* aInstance,
+                                  mozilla::TimeStamp aTime);
+  static void AsyncSmoothMSDScrollCallback(ScrollFrameHelper* aInstance,
+                                           mozilla::TimeDuration aDeltaTime);
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   * aRange is the range of allowable scroll positions around the desired
+   * aScrollPosition. Null means only aScrollPosition is allowed.
+   * This is a closed-ended range --- aRange.XMost()/aRange.YMost() are allowed.
+   */
+  void ScrollTo(nsPoint aScrollPosition, ScrollMode aMode,
+                ScrollOrigin aOrigin = ScrollOrigin::NotSpecified,
+                const nsRect* aRange = nullptr,
+                nsIScrollbarMediator::ScrollSnapMode aSnap =
+                    nsIScrollbarMediator::DISABLE_SNAP);
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void ScrollToCSSPixels(const CSSIntPoint& aScrollPosition,
+                         ScrollMode aMode = ScrollMode::Instant,
+                         nsIScrollbarMediator::ScrollSnapMode aSnap =
+                             nsIScrollbarMediator::DEFAULT,
+                         ScrollOrigin aOrigin = ScrollOrigin::NotSpecified);
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void ScrollToCSSPixelsApproximate(
+      const mozilla::CSSPoint& aScrollPosition,
+      ScrollOrigin aOrigin = ScrollOrigin::NotSpecified);
+
+  CSSIntPoint GetScrollPositionCSSPixels();
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void ScrollToImpl(nsPoint aScrollPosition, const nsRect& aRange,
+                    ScrollOrigin aOrigin = ScrollOrigin::NotSpecified);
+  void ScrollVisual();
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void ScrollBy(nsIntPoint aDelta, mozilla::ScrollUnit aUnit, ScrollMode aMode,
+                nsIntPoint* aOverflow,
+                ScrollOrigin aOrigin = ScrollOrigin::NotSpecified,
+                nsIScrollableFrame::ScrollMomentum aMomentum =
+                    nsIScrollableFrame::NOT_MOMENTUM,
+                nsIScrollbarMediator::ScrollSnapMode aSnap =
+                    nsIScrollbarMediator::DISABLE_SNAP);
+  void ScrollByCSSPixels(const CSSIntPoint& aDelta,
+                         ScrollMode aMode = ScrollMode::Instant,
+                         ScrollOrigin aOrigin = ScrollOrigin::NotSpecified,
+                         nsIScrollbarMediator::ScrollSnapMode aSnap =
+                             nsIScrollbarMediator::DEFAULT);
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void ScrollToRestoredPosition();
+
+  enum class LoadingState { Loading, Stopped, Loaded };
+
+  LoadingState GetPageLoadingState();
+
+  /**
+   * GetSnapPointForDestination determines which point to snap to after
+   * scrolling. aStartPos gives the position before scrolling and aDestination
+   * gives the position after scrolling, with no snapping. Behaviour is
+   * dependent on the value of aUnit.
+   * Returns true if a suitable snap point could be found and aDestination has
+   * been updated to a valid snapping position.
+   */
+  bool GetSnapPointForDestination(mozilla::ScrollUnit aUnit,
+                                  const nsPoint& aStartPos,
+                                  nsPoint& aDestination);
+
+  nsMargin GetScrollPadding() const;
+
+  nsSize GetLineScrollAmount() const;
+  nsSize GetPageScrollAmount() const;
+
+  mozilla::UniquePtr<mozilla::PresState> SaveState() const;
+  void RestoreState(mozilla::PresState* aState);
+
+  nsIFrame* GetScrolledFrame() const { return mScrolledFrame; }
+  nsIFrame* GetScrollbarBox(bool aVertical) const {
+    return aVertical ? mVScrollbarBox : mHScrollbarBox;
+  }
+
+  void AddScrollPositionListener(nsIScrollPositionListener* aListener) {
+    mListeners.AppendElement(aListener);
+  }
+  void RemoveScrollPositionListener(nsIScrollPositionListener* aListener) {
+    mListeners.RemoveElement(aListener);
+  }
+
+  static void SetScrollbarVisibility(nsIFrame* aScrollbar, bool aVisible);
+
+  /**
+   * GetScrolledRect is designed to encapsulate deciding which
+   * directions of overflow should be reachable by scrolling and which
+   * should not.  Callers should NOT depend on it having any particular
+   * behavior (although nsXULScrollFrame currently does).
+   *
+   * This should only be called when the scrolled frame has been
+   * reflowed with the scroll port size given in mScrollPort.
+   *
+   * Currently it allows scrolling down and to the right for
+   * nsHTMLScrollFrames with LTR directionality and for all
+   * nsXULScrollFrames, and allows scrolling down and to the left for
+   * nsHTMLScrollFrames with RTL directionality.
+   */
+  nsRect GetScrolledRect() const;
+
+  /**
+   * GetUnsnappedScrolledRectInternal is designed to encapsulate deciding which
+   * directions of overflow should be reachable by scrolling and which
+   * should not.  Callers should NOT depend on it having any particular
+   * behavior (although nsXULScrollFrame currently does).
+   *
+   * Currently it allows scrolling down and to the right for
+   * nsHTMLScrollFrames with LTR directionality and for all
+   * nsXULScrollFrames, and allows scrolling down and to the left for
+   * nsHTMLScrollFrames with RTL directionality.
+   */
+  nsRect GetUnsnappedScrolledRectInternal(const nsRect& aScrolledOverflowArea,
+                                          const nsSize& aScrollPortSize) const;
+
+  layers::ScrollDirections GetAvailableScrollingDirectionsForUserInputEvents()
+      const;
+
+  layers::ScrollDirections GetScrollbarVisibility() const {
+    layers::ScrollDirections result;
+    if (mHasHorizontalScrollbar) {
+      result += layers::ScrollDirection::eHorizontal;
+    }
+    if (mHasVerticalScrollbar) {
+      result += layers::ScrollDirection::eVertical;
+    }
+    return result;
+  }
+  nsMargin GetActualScrollbarSizes(
+      nsIScrollableFrame::ScrollbarSizesOptions aOptions =
+          nsIScrollableFrame::ScrollbarSizesOptions::NONE) const;
+  nsMargin GetDesiredScrollbarSizes(nsBoxLayoutState* aState);
+  nscoord GetNondisappearingScrollbarWidth(nsBoxLayoutState* aState,
+                                           mozilla::WritingMode aVerticalWM);
+  bool IsPhysicalLTR() const {
+    return mOuter->GetWritingMode().IsPhysicalLTR();
+  }
+  bool IsBidiLTR() const { return mOuter->GetWritingMode().IsBidiLTR(); }
+
+ private:
+  // NOTE: Use GetScrollStylesFromFrame() if you want to know `overflow`
+  // and `overflow-behavior` properties.
+  nsIFrame* GetFrameForStyle() const;
+
+  // This is the for the old unspecced scroll snap implementation.
+  ScrollSnapInfo ComputeOldScrollSnapInfo() const;
+  // This is the for the scroll snap v1 implementation.
+  ScrollSnapInfo ComputeScrollSnapInfo(
+      const Maybe<nsPoint>& aDestination) const;
+
+  bool NeedsScrollSnap() const;
+
+ public:
+  bool IsScrollbarOnRight() const;
+  bool IsScrollingActive(nsDisplayListBuilder* aBuilder) const;
+  bool IsMaybeAsynchronouslyScrolled() const {
+    // If this is true, then we'll build an ASR, and that's what we want
+    // to know I think.
+    return mWillBuildScrollableLayer;
+  }
+  bool IsMaybeScrollingActive() const;
+  void ResetScrollPositionForLayerPixelAlignment() {
+    mScrollPosForLayerPixelAlignment = GetScrollPosition();
+  }
+
+  bool ComputeCustomOverflow(mozilla::OverflowAreas& aOverflowAreas);
+
+  void UpdateSticky();
+
+  void UpdatePrevScrolledRect();
+
+  bool IsRectNearlyVisible(const nsRect& aRect) const;
+  nsRect ExpandRectToNearlyVisible(const nsRect& aRect) const;
+
+  // adjust the scrollbar rectangle aRect to account for any visible resizer.
+  // aHasResizer specifies if there is a content resizer, however this method
+  // will also check if a widget resizer is present as well.
+  void AdjustScrollbarRectForResizer(
+      nsIFrame* aFrame, nsPresContext* aPresContext, nsRect& aRect,
+      bool aHasResizer, mozilla::layers::ScrollDirection aDirection);
+  // returns true if a resizer should be visible
+  bool HasResizer() { return mResizerBox && !mCollapsedResizer; }
+  void LayoutScrollbars(nsBoxLayoutState& aState, const nsRect& aContentArea,
+                        const nsRect& aOldScrollArea);
+
+  void MarkScrollbarsDirtyForReflow() const;
+
+  bool IsAlwaysActive() const;
+  void MarkEverScrolled();
+  void MarkRecentlyScrolled();
+  void MarkNotRecentlyScrolled();
+  nsExpirationState* GetExpirationState() { return &mActivityExpirationState; }
+
+  void SetTransformingByAPZ(bool aTransforming) {
+    if (mTransformingByAPZ && !aTransforming) {
+      PostScrollEndEvent();
+    }
+    mTransformingByAPZ = aTransforming;
+    if (!mozilla::css::TextOverflow::HasClippedTextOverflow(mOuter) ||
+        mozilla::css::TextOverflow::HasBlockEllipsis(mScrolledFrame)) {
+      // If the block has some overflow marker stuff we should kick off a paint
+      // because we have special behaviour for it when APZ scrolling is active.
+      mOuter->SchedulePaint();
+    }
+  }
+  bool IsTransformingByAPZ() const { return mTransformingByAPZ; }
+  void SetScrollableByAPZ(bool aScrollable);
+  void SetZoomableByAPZ(bool aZoomable);
+  void SetHasOutOfFlowContentInsideFilter();
+
+  bool UsesOverlayScrollbars() const;
+
+  // In the case where |aDestination| is given, elements which are entirely out
+  // of view when the scroll position is moved to |aDestination| are not going
+  // to be used for snap positions.
+  ScrollSnapInfo GetScrollSnapInfo(
+      const mozilla::Maybe<nsPoint>& aDestination) const;
+
+  nsRect RestrictToRootDisplayPort(const nsRect& aDisplayportBase);
+  bool DecideScrollableLayer(nsDisplayListBuilder* aBuilder,
+                             nsRect* aVisibleRect, nsRect* aDirtyRect,
+                             bool aSetBase,
+                             bool* aDirtyRectHasBeenOverriden = nullptr);
+  void NotifyApzTransaction();
+  void NotifyApproximateFrameVisibilityUpdate(bool aIgnoreDisplayPort);
+  bool GetDisplayPortAtLastApproximateFrameVisibilityUpdate(
+      nsRect* aDisplayPort);
+
+  bool AllowDisplayPortExpiration();
+  void TriggerDisplayPortExpiration();
+  void ResetDisplayPortExpiryTimer();
+
+  void ScheduleSyntheticMouseMove();
+  static void ScrollActivityCallback(nsITimer* aTimer, void* anInstance);
+
+  void HandleScrollbarStyleSwitching();
+
+  ScrollOrigin LastScrollOrigin() const { return mLastScrollOrigin; }
+  bool IsApzAnimationInProgress() const { return mApzAnimationInProgress; }
+  ScrollGeneration CurrentScrollGeneration() const { return mScrollGeneration; }
+  nsPoint LastScrollDestination() const { return mDestination; }
+  nsTArray<ScrollPositionUpdate> GetScrollUpdates() const;
+  bool HasScrollUpdates() const { return !mScrollUpdates.IsEmpty(); }
+
+  bool IsLastScrollUpdateAnimating() const;
+  using IncludeApzAnimation = nsIScrollableFrame::IncludeApzAnimation;
+  bool IsScrollAnimating(IncludeApzAnimation = IncludeApzAnimation::Yes) const;
+
+  void ResetScrollInfoIfNeeded(const ScrollGeneration& aGeneration,
+                               bool aApzAnimationInProgress);
+  bool WantAsyncScroll() const;
+  Maybe<mozilla::layers::ScrollMetadata> ComputeScrollMetadata(
+      LayerManager* aLayerManager, const nsIFrame* aContainerReferenceFrame,
+      const Maybe<ContainerLayerParameters>& aParameters,
+      const mozilla::DisplayItemClip* aClip) const;
+  void ClipLayerToDisplayPort(
+      Layer* aLayer, const mozilla::DisplayItemClip* aClip,
+      const ContainerLayerParameters& aParameters) const;
+
+  // nsIScrollbarMediator
+  void ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                    nsIScrollbarMediator::ScrollSnapMode aSnap =
+                        nsIScrollbarMediator::DISABLE_SNAP);
+  void ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                     nsIScrollbarMediator::ScrollSnapMode aSnap =
+                         nsIScrollbarMediator::DISABLE_SNAP);
+  void ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                    nsIScrollbarMediator::ScrollSnapMode aSnap =
+                        nsIScrollbarMediator::DISABLE_SNAP);
+  void RepeatButtonScroll(nsScrollbarFrame* aScrollbar);
+  void ThumbMoved(nsScrollbarFrame* aScrollbar, nscoord aOldPos,
+                  nscoord aNewPos);
+  void ScrollbarReleased(nsScrollbarFrame* aScrollbar);
+  void ScrollByUnit(nsScrollbarFrame* aScrollbar, ScrollMode aMode,
+                    int32_t aDirection, mozilla::ScrollUnit aUnit,
+                    nsIScrollbarMediator::ScrollSnapMode aSnap =
+                        nsIScrollbarMediator::DISABLE_SNAP);
+  bool ShouldSuppressScrollbarRepaints() const {
+    return mSuppressScrollbarRepaints;
+  }
+
+  bool DragScroll(WidgetEvent* aEvent);
+
+  void AsyncScrollbarDragInitiated(uint64_t aDragBlockId,
+                                   mozilla::layers::ScrollDirection aDirection);
+  void AsyncScrollbarDragRejected();
+
+  bool IsRootScrollFrameOfDocument() const { return mIsRoot; }
+
+  bool SmoothScrollVisual(
+      const nsPoint& aVisualViewportOffset,
+      mozilla::layers::FrameMetrics::ScrollOffsetUpdateType aUpdateType);
+
+  bool IsSmoothScroll(mozilla::dom::ScrollBehavior aBehavior) const;
+
+  // Update minimum-scale size.  The minimum-scale size will be set/used only
+  // if there is overflow-x:hidden region.
+  void UpdateMinimumScaleSize(const nsRect& aScrollableOverflow,
+                              const nsSize& aICBSize);
+
+  // Return the scroll frame's "true outer size".
+  // This is mOuter->GetSize(), except when mOuter has been sized to reflect
+  // a virtual (layout) viewport in which case this returns the outer size
+  // used to size the physical (visual) viewport.
+  nsSize TrueOuterSize(nsDisplayListBuilder* aBuilder) const;
+
+  already_AddRefed<Element> MakeScrollbar(dom::NodeInfo* aNodeInfo,
+                                          bool aVertical,
+                                          AnonymousContentKey& aKey);
+
+  void AppendScrollUpdate(const ScrollPositionUpdate& aUpdate);
+
+  // owning references to the nsIAnonymousContentCreator-built content
+  nsCOMPtr<Element> mHScrollbarContent;
+  nsCOMPtr<Element> mVScrollbarContent;
+  nsCOMPtr<Element> mScrollCornerContent;
+  nsCOMPtr<Element> mResizerContent;
+
+  class ScrollEvent;
+  class ScrollEndEvent;
+  class AsyncScrollPortEvent;
+  class ScrolledAreaEvent;
+
+  RefPtr<ScrollEvent> mScrollEvent;
+  RefPtr<ScrollEndEvent> mScrollEndEvent;
+  nsRevocableEventPtr<AsyncScrollPortEvent> mAsyncScrollPortEvent;
+  nsRevocableEventPtr<ScrolledAreaEvent> mScrolledAreaEvent;
+  nsIFrame* mHScrollbarBox;
+  nsIFrame* mVScrollbarBox;
+  nsIFrame* mScrolledFrame;
+  nsIFrame* mScrollCornerBox;
+  nsIFrame* mResizerBox;
+  nsContainerFrame* mOuter;
+  const nsIFrame* mReferenceFrameDuringPainting;
+  RefPtr<AsyncScroll> mAsyncScroll;
+  RefPtr<AsyncSmoothMSDScroll> mAsyncSmoothMSDScroll;
+  RefPtr<ScrollbarActivity> mScrollbarActivity;
+  nsTArray<nsIScrollPositionListener*> mListeners;
+  ScrollOrigin mLastScrollOrigin;
+  Maybe<nsPoint> mApzSmoothScrollDestination;
+  ScrollGeneration mScrollGeneration;
+
+  nsTArray<ScrollPositionUpdate> mScrollUpdates;
+
+  // NOTE: On mobile this value might be factoring into overflow:hidden region
+  // in the case of the top level document.
+  nsRect mScrollPort;
+  nsSize mMinimumScaleSize;
+
+  // Stores the ICB size for the root document if this frame is using the
+  // minimum scale size for |mScrollPort|.
+  nsSize mICBSize;
+
+  // Where we're currently scrolling to, if we're scrolling asynchronously.
+  // If we're not in the middle of an asynchronous scroll then this is
+  // just the current scroll position. ScrollBy will choose its
+  // destination based on this value.
+  nsPoint mDestination;
+
+  // A goal position to try to scroll to as content loads. As long as mLastPos
+  // matches the current logical scroll position, we try to scroll to
+  // mRestorePos after every reflow --- because after each time content is
+  // loaded/added to the scrollable element, there will be a reflow.
+  // Note that for frames where layout and visual viewport aren't one and the
+  // same thing, this scroll position will be the logical scroll position of
+  // the *visual* viewport, as its position will be more relevant to the user.
+  nsPoint mRestorePos;
+  // The last logical position we scrolled to while trying to restore
+  // mRestorePos, or 0,0 when this is a new frame. Set to -1,-1 once we've
+  // scrolled for any reason other than trying to restore mRestorePos.
+  // Just as with mRestorePos, this position will be the logical position of
+  // the *visual* viewport where available.
+  nsPoint mLastPos;
+
+  // The latest scroll position we've sent or received from APZ. This
+  // represents the main thread's best knowledge of the APZ scroll position,
+  // and is used to calculate relative scroll offset updates.
+  nsPoint mApzScrollPos;
+
+  nsExpirationState mActivityExpirationState;
+
+  nsCOMPtr<nsITimer> mScrollActivityTimer;
+  nsPoint mScrollPosForLayerPixelAlignment;
+
+  // The scroll position where we last updated frame visibility.
+  nsPoint mLastUpdateFramesPos;
+  nsRect mDisplayPortAtLastFrameUpdate;
+
+  nsRect mPrevScrolledRect;
+
+  ScrollableLayerGuid::ViewID mScrollParentID;
+
+  // Timer to remove the displayport some time after scrolling has stopped
+  nsCOMPtr<nsITimer> mDisplayPortExpiryTimer;
+
+  ScrollAnchorContainer mAnchor;
+
+  bool mAllowScrollOriginDowngrade : 1;
+  bool mHadDisplayPortAtLastFrameUpdate : 1;
+  bool mNeverHasVerticalScrollbar : 1;
+  bool mNeverHasHorizontalScrollbar : 1;
+  bool mHasVerticalScrollbar : 1;
+  bool mHasHorizontalScrollbar : 1;
+  // If mHas(Vertical|Horizontal)Scrollbar is true then
+  // mOnlyNeed(V|H)ScrollbarToScrollVVInsideLV indicates if the only reason we
+  // need that scrollbar is to scroll the visual viewport inside the layout
+  // viewport. These scrollbars are special in that even if they are layout
+  // scrollbars they do not take up any layout space.
+  bool mOnlyNeedVScrollbarToScrollVVInsideLV : 1;
+  bool mOnlyNeedHScrollbarToScrollVVInsideLV : 1;
+  bool mFrameIsUpdatingScrollbar : 1;
+  bool mDidHistoryRestore : 1;
+  // Is this the scrollframe for the document's viewport?
+  bool mIsRoot : 1;
+  // True if we should clip all descendants, false if we should only clip
+  // descendants for which we are the containing block.
+  bool mClipAllDescendants : 1;
+  // If true, don't try to layout the scrollbars in Reflow().  This can be
+  // useful if multiple passes are involved, because we don't want to place the
+  // scrollbars at the wrong size.
+  bool mSuppressScrollbarUpdate : 1;
+  // If true, we skipped a scrollbar layout due to mSuppressScrollbarUpdate
+  // being set at some point.  That means we should lay out scrollbars even if
+  // it might not strictly be needed next time mSuppressScrollbarUpdate is
+  // false.
+  bool mSkippedScrollbarLayout : 1;
+
+  bool mHadNonInitialReflow : 1;
+  // Initially true; first call to ReflowFinished() sets it to false.
+  bool mFirstReflow : 1;
+  // State used only by PostScrollEvents so we know
+  // which overflow states have changed.
+  bool mHorizontalOverflow : 1;
+  bool mVerticalOverflow : 1;
+  bool mPostedReflowCallback : 1;
+  bool mMayHaveDirtyFixedChildren : 1;
+  // If true, need to actually update our scrollbar attributes in the
+  // reflow callback.
+  bool mUpdateScrollbarAttributes : 1;
+  // If true, we should be prepared to scroll using this scrollframe
+  // by placing descendant content into its own layer(s)
+  bool mHasBeenScrolledRecently : 1;
+  // If true, the resizer is collapsed and not displayed
+  bool mCollapsedResizer : 1;
+
+  // If true, the scroll frame should always be active because we always build
+  // a scrollable layer. Used for asynchronous scrolling.
+  bool mWillBuildScrollableLayer : 1;
+
+  // If true, the scroll frame is an ancestor of other scrolling frames, so
+  // we shouldn't expire the displayport on this scrollframe unless those
+  // descendant scrollframes also have their displayports removed.
+  bool mIsScrollParent : 1;
+
+  // If true, add clipping in ScrollFrameHelper::ClipLayerToDisplayPort.
+  // XXX this flag needs some auditing and better documentation, bug 1646686.
+  bool mAddClipRectToLayer : 1;
+
+  // True if this frame has been scrolled at least once
+  bool mHasBeenScrolled : 1;
+
+  // True if the events synthesized by OSX to produce momentum scrolling should
+  // be ignored.  Reset when the next real, non-synthesized scroll event occurs.
+  bool mIgnoreMomentumScroll : 1;
+
+  // True if the APZ is in the process of async-transforming this scrollframe,
+  // (as best as we can tell on the main thread, anyway).
+  bool mTransformingByAPZ : 1;
+
+  // True if APZ can scroll this frame asynchronously (i.e. it has an APZC
+  // set up for this frame and it's not a scrollinfo layer).
+  bool mScrollableByAPZ : 1;
+
+  // True if the APZ is allowed to zoom this scrollframe.
+  bool mZoomableByAPZ : 1;
+
+  // True if the scroll frame contains out-of-flow content and is inside
+  // a CSS filter.
+  bool mHasOutOfFlowContentInsideFilter : 1;
+
+  // True if we don't want the scrollbar to repaint itself right now.
+  bool mSuppressScrollbarRepaints : 1;
+
+  // True if we are using the minimum scale size instead of ICB for scroll port.
+  bool mIsUsingMinimumScaleSize : 1;
+
+  // True if the minimum scale size has been changed since the last reflow.
+  bool mMinimumScaleSizeChanged : 1;
+
+  // True if we're processing an scroll event.
+  bool mProcessingScrollEvent : 1;
+
+  // Whether an APZ animation is in progress. Note that this is only set to true
+  // when repainted via APZ, which means that there may be a request for an APZ
+  // animation in flight for example, while this is still false. In order to
+  // answer "is an APZ animation in the process of starting or in progress" you
+  // need to check mScrollUpdates, mApzAnimationRequested, and this bit.
+  bool mApzAnimationInProgress : 1;
+  // This is true from the time a scroll animation is requested of APZ to the
+  // time that APZ responds with an up-to-date repaint request. More precisely,
+  // this is flipped to true if a repaint request is dispatched to APZ where
+  // the most recent scroll request is a smooth scroll, and it is cleared when
+  // mApzAnimationInProgress is updated.
+  bool mApzAnimationRequested : 1;
+
+  // Whether we need to reclamp the visual viewport offset in ReflowFinished.
+  bool mReclampVVOffsetInReflowFinished : 1;
+
+  mozilla::layout::ScrollVelocityQueue mVelocityQueue;
+
+ protected:
+  class AutoScrollbarRepaintSuppression;
+  friend class AutoScrollbarRepaintSuppression;
+  class AutoScrollbarRepaintSuppression {
+   public:
+    AutoScrollbarRepaintSuppression(ScrollFrameHelper* aHelper,
+                                    AutoWeakFrame& aWeakOuter, bool aSuppress)
+        : mHelper(aHelper),
+          mWeakOuter(aWeakOuter),
+          mOldSuppressValue(aHelper->mSuppressScrollbarRepaints) {
+      mHelper->mSuppressScrollbarRepaints = aSuppress;
+    }
+
+    ~AutoScrollbarRepaintSuppression() {
+      if (mWeakOuter.IsAlive()) {
+        mHelper->mSuppressScrollbarRepaints = mOldSuppressValue;
+      }
+    }
+
+   private:
+    ScrollFrameHelper* mHelper;
+    AutoWeakFrame& mWeakOuter;
+    bool mOldSuppressValue;
+  };
+
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void ScrollToWithOrigin(nsPoint aScrollPosition, ScrollMode aMode,
+                          ScrollOrigin aOrigin, const nsRect* aRange,
+                          nsIScrollbarMediator::ScrollSnapMode aSnap =
+                              nsIScrollbarMediator::DISABLE_SNAP);
+
+  void CompleteAsyncScroll(const nsRect& aRange,
+                           ScrollOrigin aOrigin = ScrollOrigin::NotSpecified);
+
+  bool HasPluginFrames();
+  bool HasPerspective() const { return mOuter->ChildrenHavePerspective(); }
+  bool HasBgAttachmentLocal() const;
+  mozilla::StyleDirection GetScrolledFrameDir() const;
+
+  // Ask APZ to smooth scroll to |aDestination|.
+  // This method does not clamp the destination; callers should clamp it to
+  // either the layout or the visual scroll range (APZ will happily smooth
+  // scroll to either).
+  void ApzSmoothScrollTo(const nsPoint& aDestination, ScrollOrigin aOrigin);
+
+  // Removes any RefreshDriver observers we might have registered.
+  void RemoveObservers();
+};
+
+}  // namespace mozilla
+
+/**
+ * The scroll frame creates and manages the scrolling view
+ *
+ * It only supports having a single child frame that typically is an area
+ * frame, but doesn't have to be. The child frame must have a view, though
+ *
+ * Scroll frames don't support incremental changes, i.e. you can't replace
+ * or remove the scrolled frame
+ */
+class nsHTMLScrollFrame : public nsContainerFrame,
+                          public nsIScrollableFrame,
+                          public nsIAnonymousContentCreator,
+                          public nsIStatefulFrame {
+ public:
+  typedef mozilla::ScrollFrameHelper ScrollFrameHelper;
+  typedef mozilla::CSSIntPoint CSSIntPoint;
+  typedef mozilla::ScrollReflowInput ScrollReflowInput;
+  typedef mozilla::layout::ScrollAnchorContainer ScrollAnchorContainer;
+  friend nsHTMLScrollFrame* NS_NewHTMLScrollFrame(
+      mozilla::PresShell* aPresShell, ComputedStyle* aStyle, bool aIsRoot);
+
+  NS_DECL_QUERYFRAME
+  NS_DECL_FRAMEARENA_HELPERS(nsHTMLScrollFrame)
+
+  void BuildDisplayList(nsDisplayListBuilder* aBuilder,
+                        const nsDisplayListSet& aLists) override {
+    mHelper.BuildDisplayList(aBuilder, aLists);
+  }
+
+  bool TryLayout(ScrollReflowInput* aState, ReflowOutput* aKidMetrics,
+                 bool aAssumeVScroll, bool aAssumeHScroll, bool aForce);
+  bool ScrolledContentDependsOnHeight(ScrollReflowInput* aState);
+  void ReflowScrolledFrame(ScrollReflowInput* aState, bool aAssumeHScroll,
+                           bool aAssumeVScroll, ReflowOutput* aMetrics);
+  void ReflowContents(ScrollReflowInput* aState,
+                      const ReflowOutput& aDesiredSize);
+  void PlaceScrollArea(ScrollReflowInput& aState,
+                       const nsPoint& aScrollPosition);
+  nscoord GetIntrinsicVScrollbarWidth(gfxContext* aRenderingContext);
+
+  bool GetBorderRadii(const nsSize& aFrameSize, const nsSize& aBorderArea,
+                      Sides aSkipSides, nscoord aRadii[8]) const final {
+    return mHelper.GetBorderRadii(aFrameSize, aBorderArea, aSkipSides, aRadii);
+  }
+
+  nscoord GetMinISize(gfxContext* aRenderingContext) override;
+  nscoord GetPrefISize(gfxContext* aRenderingContext) override;
+  nsresult GetXULPadding(nsMargin& aPadding) final;
+  bool IsXULCollapsed() final;
+
+  void Reflow(nsPresContext* aPresContext, ReflowOutput& aDesiredSize,
+              const ReflowInput& aReflowInput,
+              nsReflowStatus& aStatus) override;
+  void DidReflow(nsPresContext* aPresContext,
+                 const ReflowInput* aReflowInput) override;
+
+  bool ComputeCustomOverflow(mozilla::OverflowAreas& aOverflowAreas) final {
+    return mHelper.ComputeCustomOverflow(aOverflowAreas);
+  }
+
+  nscoord GetLogicalBaseline(mozilla::WritingMode aWritingMode) const final;
+
+  bool GetVerticalAlignBaseline(mozilla::WritingMode aWM,
+                                nscoord* aBaseline) const final {
+    NS_ASSERTION(!aWM.IsOrthogonalTo(GetWritingMode()),
+                 "You should only call this on frames with a WM that's "
+                 "parallel to aWM");
+    *aBaseline = GetLogicalBaseline(aWM);
+    return true;
+  }
+
+  // Recomputes the scrollable overflow area we store in the helper to take
+  // children that are affected by perpsective set on the outer frame and scroll
+  // at different rates.
+  void AdjustForPerspective(nsRect& aScrollableOverflow);
+
+  // Called to set the child frames. We typically have three: the scroll area,
+  // the vertical scrollbar, and the horizontal scrollbar.
+  void SetInitialChildList(ChildListID aListID,
+                           nsFrameList& aChildList) override;
+  void AppendFrames(ChildListID aListID, nsFrameList& aFrameList) final;
+  void InsertFrames(ChildListID aListID, nsIFrame* aPrevFrame,
+                    const nsLineList::iterator* aPrevFrameLine,
+                    nsFrameList& aFrameList) final;
+  void RemoveFrame(ChildListID aListID, nsIFrame* aOldFrame) final;
+
+  void DestroyFrom(nsIFrame* aDestructRoot, PostDestroyData&) override;
+
+  nsIScrollableFrame* GetScrollTargetFrame() const final {
+    return const_cast<nsHTMLScrollFrame*>(this);
+  }
+
+  nsContainerFrame* GetContentInsertionFrame() override {
+    return mHelper.GetScrolledFrame()->GetContentInsertionFrame();
+  }
+
+  bool DoesClipChildrenInBothAxes() final { return true; }
+
+  nsPoint GetPositionOfChildIgnoringScrolling(const nsIFrame* aChild) final {
+    nsPoint pt = aChild->GetPosition();
+    if (aChild == mHelper.GetScrolledFrame()) pt += GetScrollPosition();
+    return pt;
+  }
+
+  // nsIAnonymousContentCreator
+  nsresult CreateAnonymousContent(nsTArray<ContentInfo>&) final;
+  void AppendAnonymousContentTo(nsTArray<nsIContent*>&, uint32_t aFilter) final;
+
+  // nsIScrollableFrame
+  nsIFrame* GetScrolledFrame() const final {
+    return mHelper.GetScrolledFrame();
+  }
+  mozilla::ScrollStyles GetScrollStyles() const override {
+    return mHelper.GetScrollStylesFromFrame();
+  }
+  bool IsForTextControlWithNoScrollbars() const final {
+    return mHelper.IsForTextControlWithNoScrollbars();
+  }
+  mozilla::layers::OverscrollBehaviorInfo GetOverscrollBehaviorInfo()
+      const final {
+    return mHelper.GetOverscrollBehaviorInfo();
+  }
+  mozilla::layers::ScrollDirections
+  GetAvailableScrollingDirectionsForUserInputEvents() const final {
+    return mHelper.GetAvailableScrollingDirectionsForUserInputEvents();
+  }
+  mozilla::layers::ScrollDirections GetScrollbarVisibility() const final {
+    return mHelper.GetScrollbarVisibility();
+  }
+  nsMargin GetActualScrollbarSizes(
+      nsIScrollableFrame::ScrollbarSizesOptions aOptions =
+          nsIScrollableFrame::ScrollbarSizesOptions::NONE) const final {
+    return mHelper.GetActualScrollbarSizes(aOptions);
+  }
+  nsMargin GetDesiredScrollbarSizes(nsBoxLayoutState* aState) final {
+    return mHelper.GetDesiredScrollbarSizes(aState);
+  }
+  nsMargin GetDesiredScrollbarSizes(nsPresContext* aPresContext,
+                                    gfxContext* aRC) final {
+    nsBoxLayoutState bls(aPresContext, aRC, 0);
+    return GetDesiredScrollbarSizes(&bls);
+  }
+  nscoord GetNondisappearingScrollbarWidth(nsPresContext* aPresContext,
+                                           gfxContext* aRC,
+                                           mozilla::WritingMode aWM) final {
+    nsBoxLayoutState bls(aPresContext, aRC, 0);
+    return mHelper.GetNondisappearingScrollbarWidth(&bls, aWM);
+  }
+  nsSize GetLayoutSize() const final { return mHelper.GetLayoutSize(); }
+  nsRect GetScrolledRect() const final { return mHelper.GetScrolledRect(); }
+  nsRect GetScrollPortRect() const final { return mHelper.GetScrollPortRect(); }
+  nsPoint GetScrollPosition() const final {
+    return mHelper.GetScrollPosition();
+  }
+  nsPoint GetLogicalScrollPosition() const final {
+    return mHelper.GetLogicalScrollPosition();
+  }
+  nsRect GetScrollRange() const final { return mHelper.GetLayoutScrollRange(); }
+  nsSize GetVisualViewportSize() const final {
+    return mHelper.GetVisualViewportSize();
+  }
+  nsPoint GetVisualViewportOffset() const final {
+    return mHelper.GetVisualViewportOffset();
+  }
+  bool SetVisualViewportOffset(const nsPoint& aOffset, bool aRepaint) final {
+    return mHelper.SetVisualViewportOffset(aOffset, aRepaint);
+  }
+  nsRect GetVisualScrollRange() const final {
+    return mHelper.GetVisualScrollRange();
+  }
+  nsRect GetScrollRangeForUserInputEvents() const final {
+    return mHelper.GetScrollRangeForUserInputEvents();
+  }
+  nsSize GetLineScrollAmount() const final {
+    return mHelper.GetLineScrollAmount();
+  }
+  nsSize GetPageScrollAmount() const final {
+    return mHelper.GetPageScrollAmount();
+  }
+  nsMargin GetScrollPadding() const final { return mHelper.GetScrollPadding(); }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void ScrollTo(nsPoint aScrollPosition, ScrollMode aMode,
+                const nsRect* aRange = nullptr,
+                nsIScrollbarMediator::ScrollSnapMode aSnap =
+                    nsIScrollbarMediator::DISABLE_SNAP) final {
+    mHelper.ScrollTo(aScrollPosition, aMode, ScrollOrigin::Other, aRange,
+                     aSnap);
+  }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void ScrollToCSSPixels(
+      const CSSIntPoint& aScrollPosition,
+      ScrollMode aMode = ScrollMode::Instant,
+      nsIScrollbarMediator::ScrollSnapMode aSnap =
+          nsIScrollbarMediator::DEFAULT,
+      ScrollOrigin aOrigin = ScrollOrigin::NotSpecified) final {
+    mHelper.ScrollToCSSPixels(aScrollPosition, aMode, aSnap, aOrigin);
+  }
+  void ScrollToCSSPixelsApproximate(
+      const mozilla::CSSPoint& aScrollPosition,
+      ScrollOrigin aOrigin = ScrollOrigin::NotSpecified) final {
+    mHelper.ScrollToCSSPixelsApproximate(aScrollPosition, aOrigin);
+  }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  CSSIntPoint GetScrollPositionCSSPixels() final {
+    return mHelper.GetScrollPositionCSSPixels();
+  }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void ScrollBy(nsIntPoint aDelta, mozilla::ScrollUnit aUnit, ScrollMode aMode,
+                nsIntPoint* aOverflow,
+                ScrollOrigin aOrigin = ScrollOrigin::NotSpecified,
+                nsIScrollableFrame::ScrollMomentum aMomentum =
+                    nsIScrollableFrame::NOT_MOMENTUM,
+                nsIScrollbarMediator::ScrollSnapMode aSnap =
+                    nsIScrollbarMediator::DISABLE_SNAP) final {
+    mHelper.ScrollBy(aDelta, aUnit, aMode, aOverflow, aOrigin, aMomentum,
+                     aSnap);
+  }
+  void ScrollByCSSPixels(const CSSIntPoint& aDelta,
+                         ScrollMode aMode = ScrollMode::Instant,
+                         ScrollOrigin aOrigin = ScrollOrigin::NotSpecified,
+                         nsIScrollbarMediator::ScrollSnapMode aSnap =
+                             nsIScrollbarMediator::DEFAULT) final {
+    mHelper.ScrollByCSSPixels(aDelta, aMode, aOrigin, aSnap);
+  }
+  void ScrollSnap() final { mHelper.ScrollSnap(); }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void ScrollToRestoredPosition() final { mHelper.ScrollToRestoredPosition(); }
+  void AddScrollPositionListener(nsIScrollPositionListener* aListener) final {
+    mHelper.AddScrollPositionListener(aListener);
+  }
+  void RemoveScrollPositionListener(
+      nsIScrollPositionListener* aListener) final {
+    mHelper.RemoveScrollPositionListener(aListener);
+  }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void CurPosAttributeChanged(nsIContent* aChild) final {
+    mHelper.CurPosAttributeChanged(aChild);
+  }
+  NS_IMETHOD PostScrolledAreaEventForCurrentArea() final {
+    mHelper.PostScrolledAreaEvent();
+    return NS_OK;
+  }
+  bool IsScrollingActive(nsDisplayListBuilder* aBuilder) final {
+    return mHelper.IsScrollingActive(aBuilder);
+  }
+  bool IsMaybeScrollingActive() const final {
+    return mHelper.IsMaybeScrollingActive();
+  }
+  bool IsMaybeAsynchronouslyScrolled() final {
+    return mHelper.IsMaybeAsynchronouslyScrolled();
+  }
+  void ResetScrollPositionForLayerPixelAlignment() final {
+    mHelper.ResetScrollPositionForLayerPixelAlignment();
+  }
+  bool DidHistoryRestore() const final { return mHelper.mDidHistoryRestore; }
+  void ClearDidHistoryRestore() final { mHelper.mDidHistoryRestore = false; }
+  void MarkEverScrolled() final { mHelper.MarkEverScrolled(); }
+  bool IsRectNearlyVisible(const nsRect& aRect) final {
+    return mHelper.IsRectNearlyVisible(aRect);
+  }
+  nsRect ExpandRectToNearlyVisible(const nsRect& aRect) const final {
+    return mHelper.ExpandRectToNearlyVisible(aRect);
+  }
+  ScrollOrigin LastScrollOrigin() final { return mHelper.LastScrollOrigin(); }
+  bool IsScrollAnimating(IncludeApzAnimation aIncludeApz) final {
+    return mHelper.IsScrollAnimating(aIncludeApz);
+  }
+  mozilla::ScrollGeneration CurrentScrollGeneration() const final {
+    return mHelper.CurrentScrollGeneration();
+  }
+  nsPoint LastScrollDestination() final {
+    return mHelper.LastScrollDestination();
+  }
+  nsTArray<mozilla::ScrollPositionUpdate> GetScrollUpdates() const final {
+    return mHelper.GetScrollUpdates();
+  }
+  bool HasScrollUpdates() const final { return mHelper.HasScrollUpdates(); }
+  void ResetScrollInfoIfNeeded(const mozilla::ScrollGeneration& aGeneration,
+                               bool aApzAnimationInProgress) final {
+    mHelper.ResetScrollInfoIfNeeded(aGeneration, aApzAnimationInProgress);
+  }
+  bool WantAsyncScroll() const final { return mHelper.WantAsyncScroll(); }
+  mozilla::Maybe<mozilla::layers::ScrollMetadata> ComputeScrollMetadata(
+      LayerManager* aLayerManager, const nsIFrame* aContainerReferenceFrame,
+      const Maybe<ContainerLayerParameters>& aParameters,
+      const mozilla::DisplayItemClip* aClip) const final {
+    return mHelper.ComputeScrollMetadata(
+        aLayerManager, aContainerReferenceFrame, aParameters, aClip);
+  }
+  void ClipLayerToDisplayPort(
+      Layer* aLayer, const mozilla::DisplayItemClip* aClip,
+      const ContainerLayerParameters& aParameters) const final {
+    mHelper.ClipLayerToDisplayPort(aLayer, aClip, aParameters);
+  }
+  void MarkScrollbarsDirtyForReflow() const final {
+    mHelper.MarkScrollbarsDirtyForReflow();
+  }
+  void UpdateScrollbarPosition() final { mHelper.UpdateScrollbarPosition(); }
+  bool DecideScrollableLayer(nsDisplayListBuilder* aBuilder,
+                             nsRect* aVisibleRect, nsRect* aDirtyRect,
+                             bool aSetBase) final {
+    return mHelper.DecideScrollableLayer(aBuilder, aVisibleRect, aDirtyRect,
+                                         aSetBase);
+  }
+  void NotifyApzTransaction() final { mHelper.NotifyApzTransaction(); }
+  void NotifyApproximateFrameVisibilityUpdate(bool aIgnoreDisplayPort) final {
+    mHelper.NotifyApproximateFrameVisibilityUpdate(aIgnoreDisplayPort);
+  }
+  bool GetDisplayPortAtLastApproximateFrameVisibilityUpdate(
+      nsRect* aDisplayPort) final {
+    return mHelper.GetDisplayPortAtLastApproximateFrameVisibilityUpdate(
+        aDisplayPort);
+  }
+  void TriggerDisplayPortExpiration() final {
+    mHelper.TriggerDisplayPortExpiration();
+  }
+
+  // nsIStatefulFrame
+  mozilla::UniquePtr<mozilla::PresState> SaveState() final {
+    return mHelper.SaveState();
+  }
+  NS_IMETHOD RestoreState(mozilla::PresState* aState) final {
+    NS_ENSURE_ARG_POINTER(aState);
+    mHelper.RestoreState(aState);
+    return NS_OK;
+  }
+
+  // nsIScrollbarMediator
+  void ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                    nsIScrollbarMediator::ScrollSnapMode aSnap =
+                        nsIScrollbarMediator::DISABLE_SNAP) final {
+    mHelper.ScrollByPage(aScrollbar, aDirection, aSnap);
+  }
+  void ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                     nsIScrollbarMediator::ScrollSnapMode aSnap =
+                         nsIScrollbarMediator::DISABLE_SNAP) final {
+    mHelper.ScrollByWhole(aScrollbar, aDirection, aSnap);
+  }
+  void ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                    nsIScrollbarMediator::ScrollSnapMode aSnap =
+                        nsIScrollbarMediator::DISABLE_SNAP) final {
+    mHelper.ScrollByLine(aScrollbar, aDirection, aSnap);
+  }
+  void RepeatButtonScroll(nsScrollbarFrame* aScrollbar) final {
+    mHelper.RepeatButtonScroll(aScrollbar);
+  }
+  void ThumbMoved(nsScrollbarFrame* aScrollbar, nscoord aOldPos,
+                  nscoord aNewPos) final {
+    mHelper.ThumbMoved(aScrollbar, aOldPos, aNewPos);
+  }
+  void ScrollbarReleased(nsScrollbarFrame* aScrollbar) final {
+    mHelper.ScrollbarReleased(aScrollbar);
+  }
+  void VisibilityChanged(bool aVisible) final {}
+  nsIFrame* GetScrollbarBox(bool aVertical) final {
+    return mHelper.GetScrollbarBox(aVertical);
+  }
+  void ScrollbarActivityStarted() const final;
+  void ScrollbarActivityStopped() const final;
+
+  bool IsScrollbarOnRight() const final { return mHelper.IsScrollbarOnRight(); }
+
+  bool ShouldSuppressScrollbarRepaints() const final {
+    return mHelper.ShouldSuppressScrollbarRepaints();
+  }
+
+  void SetTransformingByAPZ(bool aTransforming) final {
+    mHelper.SetTransformingByAPZ(aTransforming);
+  }
+  bool IsTransformingByAPZ() const final {
+    return mHelper.IsTransformingByAPZ();
+  }
+  void SetScrollableByAPZ(bool aScrollable) final {
+    mHelper.SetScrollableByAPZ(aScrollable);
+  }
+  void SetZoomableByAPZ(bool aZoomable) final {
+    mHelper.SetZoomableByAPZ(aZoomable);
+  }
+  void SetHasOutOfFlowContentInsideFilter() final {
+    mHelper.SetHasOutOfFlowContentInsideFilter();
+  }
+
+  ScrollSnapInfo GetScrollSnapInfo() const final {
+    return mHelper.GetScrollSnapInfo(Nothing());
+  }
+
+  bool DragScroll(mozilla::WidgetEvent* aEvent) final {
+    return mHelper.DragScroll(aEvent);
+  }
+
+  void AsyncScrollbarDragInitiated(
+      uint64_t aDragBlockId,
+      mozilla::layers::ScrollDirection aDirection) final {
+    return mHelper.AsyncScrollbarDragInitiated(aDragBlockId, aDirection);
+  }
+
+  void AsyncScrollbarDragRejected() final {
+    return mHelper.AsyncScrollbarDragRejected();
+  }
+
+  bool IsRootScrollFrameOfDocument() const final {
+    return mHelper.IsRootScrollFrameOfDocument();
+  }
+
+  const ScrollAnchorContainer* Anchor() const final { return &mHelper.mAnchor; }
+
+  ScrollAnchorContainer* Anchor() final { return &mHelper.mAnchor; }
+
+  // Return the scrolled frame.
+  void AppendDirectlyOwnedAnonBoxes(nsTArray<OwnedAnonBox>& aResult) final {
+    aResult.AppendElement(OwnedAnonBox(mHelper.GetScrolledFrame()));
+  }
+
+  bool SmoothScrollVisual(
+      const nsPoint& aVisualViewportOffset,
+      mozilla::layers::FrameMetrics::ScrollOffsetUpdateType aUpdateType) final {
+    return mHelper.SmoothScrollVisual(aVisualViewportOffset, aUpdateType);
+  }
+
+  bool IsSmoothScroll(mozilla::dom::ScrollBehavior aBehavior) const final {
+    return mHelper.IsSmoothScroll(aBehavior);
+  }
+
+#ifdef DEBUG_FRAME_DUMP
+  nsresult GetFrameName(nsAString& aResult) const override;
+#endif
+
+#ifdef ACCESSIBILITY
+  mozilla::a11y::AccType AccessibleType() override;
+#endif
+
+ protected:
+  nsHTMLScrollFrame(ComputedStyle* aStyle, nsPresContext* aPresContext,
+                    bool aIsRoot)
+      : nsHTMLScrollFrame(aStyle, aPresContext, kClassID, aIsRoot) {}
+
+  nsHTMLScrollFrame(ComputedStyle* aStyle, nsPresContext* aPresContext,
+                    nsIFrame::ClassID aID, bool aIsRoot);
+  void SetSuppressScrollbarUpdate(bool aSuppress) {
+    mHelper.mSuppressScrollbarUpdate = aSuppress;
+  }
+  bool GuessHScrollbarNeeded(const ScrollReflowInput& aState);
+  bool GuessVScrollbarNeeded(const ScrollReflowInput& aState);
+
+  bool IsScrollbarUpdateSuppressed() const {
+    return mHelper.mSuppressScrollbarUpdate;
+  }
+
+  // Return whether we're in an "initial" reflow.  Some reflows with
+  // NS_FRAME_FIRST_REFLOW set are NOT "initial" as far as we're concerned.
+  bool InInitialReflow() const;
+
+  /**
+   * Override this to return false if computed bsize/min-bsize/max-bsize
+   * should NOT be propagated to child content.
+   * nsListControlFrame uses this.
+   */
+  virtual bool ShouldPropagateComputedBSizeToScrolledContent() const {
+    return true;
+  }
+
+ private:
+  friend class mozilla::ScrollFrameHelper;
+  ScrollFrameHelper mHelper;
+};
+
+/**
+ * The scroll frame creates and manages the scrolling view
+ *
+ * It only supports having a single child frame that typically is an area
+ * frame, but doesn't have to be. The child frame must have a view, though
+ *
+ * Scroll frames don't support incremental changes, i.e. you can't replace
+ * or remove the scrolled frame
+ */
+class nsXULScrollFrame final : public nsBoxFrame,
+                               public nsIScrollableFrame,
+                               public nsIAnonymousContentCreator,
+                               public nsIStatefulFrame {
+ public:
+  typedef mozilla::ScrollFrameHelper ScrollFrameHelper;
+  typedef mozilla::CSSIntPoint CSSIntPoint;
+  typedef mozilla::layout::ScrollAnchorContainer ScrollAnchorContainer;
+
+  NS_DECL_QUERYFRAME
+  NS_DECL_FRAMEARENA_HELPERS(nsXULScrollFrame)
+
+  friend nsXULScrollFrame* NS_NewXULScrollFrame(mozilla::PresShell* aPresShell,
+                                                ComputedStyle* aStyle,
+                                                bool aIsRoot,
+                                                bool aClipAllDescendants);
+
+  void BuildDisplayList(nsDisplayListBuilder* aBuilder,
+                        const nsDisplayListSet& aLists) final {
+    mHelper.BuildDisplayList(aBuilder, aLists);
+  }
+
+  // XXXldb Is this actually used?
+#if 0
+  nscoord GetMinISize(gfxContext *aRenderingContext) final;
+#endif
+
+  bool ComputeCustomOverflow(mozilla::OverflowAreas& aOverflowAreas) final {
+    return mHelper.ComputeCustomOverflow(aOverflowAreas);
+  }
+
+  bool GetVerticalAlignBaseline(mozilla::WritingMode aWM,
+                                nscoord* aBaseline) const final {
+    *aBaseline = GetLogicalBaseline(aWM);
+    return true;
+  }
+
+  // Called to set the child frames. We typically have three: the scroll area,
+  // the vertical scrollbar, and the horizontal scrollbar.
+  void SetInitialChildList(ChildListID aListID, nsFrameList& aChildList) final;
+  void AppendFrames(ChildListID aListID, nsFrameList& aFrameList) final;
+  void InsertFrames(ChildListID aListID, nsIFrame* aPrevFrame,
+                    const nsLineList::iterator* aPrevFrameLine,
+                    nsFrameList& aFrameList) final;
+  void RemoveFrame(ChildListID aListID, nsIFrame* aOldFrame) final;
+
+  void DestroyFrom(nsIFrame* aDestructRoot,
+                   PostDestroyData& aPostDestroyData) final;
+
+  nsIScrollableFrame* GetScrollTargetFrame() const final {
+    return const_cast<nsXULScrollFrame*>(this);
+  }
+
+  nsContainerFrame* GetContentInsertionFrame() final {
+    return mHelper.GetScrolledFrame()->GetContentInsertionFrame();
+  }
+
+  bool DoesClipChildrenInBothAxes() final { return true; }
+
+  nsPoint GetPositionOfChildIgnoringScrolling(const nsIFrame* aChild) final {
+    nsPoint pt = aChild->GetPosition();
+    if (aChild == mHelper.GetScrolledFrame())
+      pt += mHelper.GetLogicalScrollPosition();
+    return pt;
+  }
+
+  // nsIAnonymousContentCreator
+  nsresult CreateAnonymousContent(nsTArray<ContentInfo>& aElements) final;
+  void AppendAnonymousContentTo(nsTArray<nsIContent*>& aElements,
+                                uint32_t aFilter) final;
+
+  nsSize GetXULMinSize(nsBoxLayoutState& aBoxLayoutState) final;
+  nsSize GetXULPrefSize(nsBoxLayoutState& aBoxLayoutState) final;
+  nsSize GetXULMaxSize(nsBoxLayoutState& aBoxLayoutState) final;
+  nscoord GetXULBoxAscent(nsBoxLayoutState& aBoxLayoutState) final;
+
+  NS_IMETHOD DoXULLayout(nsBoxLayoutState& aBoxLayoutState) final;
+  nsresult GetXULPadding(nsMargin& aPadding) final;
+
+  bool GetBorderRadii(const nsSize& aFrameSize, const nsSize& aBorderArea,
+                      Sides aSkipSides, nscoord aRadii[8]) const final {
+    return mHelper.GetBorderRadii(aFrameSize, aBorderArea, aSkipSides, aRadii);
+  }
+
+  nsresult XULLayout(nsBoxLayoutState& aState);
+  void LayoutScrollArea(nsBoxLayoutState& aState,
+                        const nsPoint& aScrollPosition);
+
+  static bool AddRemoveScrollbar(bool& aHasScrollbar, nscoord& aXY,
+                                 nscoord& aSize, nscoord aSbSize,
+                                 bool aOnRightOrBottom, bool aAdd);
+
+  bool AddRemoveScrollbar(nsBoxLayoutState& aState, bool aOnRightOrBottom,
+                          bool aHorizontal, bool aAdd);
+
+  bool AddHorizontalScrollbar(nsBoxLayoutState& aState, bool aOnBottom);
+  bool AddVerticalScrollbar(nsBoxLayoutState& aState, bool aOnRight);
+  void RemoveHorizontalScrollbar(nsBoxLayoutState& aState, bool aOnBottom);
+  void RemoveVerticalScrollbar(nsBoxLayoutState& aState, bool aOnRight);
+
+  static void AdjustReflowInputForPrintPreview(nsBoxLayoutState& aState,
+                                               bool& aSetBack);
+  static void AdjustReflowInputBack(nsBoxLayoutState& aState, bool aSetBack);
+
+  // nsIScrollableFrame
+  nsIFrame* GetScrolledFrame() const final {
+    return mHelper.GetScrolledFrame();
+  }
+  mozilla::ScrollStyles GetScrollStyles() const final {
+    return mHelper.GetScrollStylesFromFrame();
+  }
+  bool IsForTextControlWithNoScrollbars() const final {
+    return mHelper.IsForTextControlWithNoScrollbars();
+  }
+  mozilla::layers::OverscrollBehaviorInfo GetOverscrollBehaviorInfo()
+      const final {
+    return mHelper.GetOverscrollBehaviorInfo();
+  }
+  mozilla::layers::ScrollDirections
+  GetAvailableScrollingDirectionsForUserInputEvents() const final {
+    return mHelper.GetAvailableScrollingDirectionsForUserInputEvents();
+  }
+  mozilla::layers::ScrollDirections GetScrollbarVisibility() const final {
+    return mHelper.GetScrollbarVisibility();
+  }
+  nsMargin GetActualScrollbarSizes(
+      nsIScrollableFrame::ScrollbarSizesOptions aOptions =
+          nsIScrollableFrame::ScrollbarSizesOptions::NONE) const final {
+    return mHelper.GetActualScrollbarSizes(aOptions);
+  }
+  nsMargin GetDesiredScrollbarSizes(nsBoxLayoutState* aState) final {
+    return mHelper.GetDesiredScrollbarSizes(aState);
+  }
+  nsMargin GetDesiredScrollbarSizes(nsPresContext* aPresContext,
+                                    gfxContext* aRC) final {
+    nsBoxLayoutState bls(aPresContext, aRC, 0);
+    return GetDesiredScrollbarSizes(&bls);
+  }
+  nscoord GetNondisappearingScrollbarWidth(nsPresContext* aPresContext,
+                                           gfxContext* aRC,
+                                           mozilla::WritingMode aWM) final {
+    nsBoxLayoutState bls(aPresContext, aRC, 0);
+    return mHelper.GetNondisappearingScrollbarWidth(&bls, aWM);
+  }
+  nsSize GetLayoutSize() const final { return mHelper.GetLayoutSize(); }
+  nsRect GetScrolledRect() const final { return mHelper.GetScrolledRect(); }
+  nsRect GetScrollPortRect() const final { return mHelper.GetScrollPortRect(); }
+  nsPoint GetScrollPosition() const final {
+    return mHelper.GetScrollPosition();
+  }
+  nsPoint GetLogicalScrollPosition() const final {
+    return mHelper.GetLogicalScrollPosition();
+  }
+  nsRect GetScrollRange() const final { return mHelper.GetLayoutScrollRange(); }
+  nsSize GetVisualViewportSize() const final {
+    return mHelper.GetVisualViewportSize();
+  }
+  nsPoint GetVisualViewportOffset() const final {
+    return mHelper.GetVisualViewportOffset();
+  }
+  bool SetVisualViewportOffset(const nsPoint& aOffset, bool aRepaint) final {
+    return mHelper.SetVisualViewportOffset(aOffset, aRepaint);
+  }
+  nsRect GetVisualScrollRange() const final {
+    return mHelper.GetVisualScrollRange();
+  }
+  nsRect GetScrollRangeForUserInputEvents() const final {
+    return mHelper.GetScrollRangeForUserInputEvents();
+  }
+  nsSize GetLineScrollAmount() const final {
+    return mHelper.GetLineScrollAmount();
+  }
+  nsSize GetPageScrollAmount() const final {
+    return mHelper.GetPageScrollAmount();
+  }
+  nsMargin GetScrollPadding() const final { return mHelper.GetScrollPadding(); }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void ScrollTo(
+      nsPoint aScrollPosition, ScrollMode aMode, const nsRect* aRange = nullptr,
+      ScrollSnapMode aSnap = nsIScrollbarMediator::DISABLE_SNAP) final {
+    mHelper.ScrollTo(aScrollPosition, aMode, ScrollOrigin::Other, aRange,
+                     aSnap);
+  }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void ScrollToCSSPixels(
+      const CSSIntPoint& aScrollPosition,
+      ScrollMode aMode = ScrollMode::Instant,
+      nsIScrollbarMediator::ScrollSnapMode aSnap =
+          nsIScrollbarMediator::DISABLE_SNAP,
+      ScrollOrigin aOrigin = ScrollOrigin::NotSpecified) final {
+    mHelper.ScrollToCSSPixels(aScrollPosition, aMode, aSnap, aOrigin);
+  }
+  void ScrollToCSSPixelsApproximate(
+      const mozilla::CSSPoint& aScrollPosition,
+      ScrollOrigin aOrigin = ScrollOrigin::NotSpecified) final {
+    mHelper.ScrollToCSSPixelsApproximate(aScrollPosition, aOrigin);
+  }
+  CSSIntPoint GetScrollPositionCSSPixels() final {
+    return mHelper.GetScrollPositionCSSPixels();
+  }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void ScrollBy(nsIntPoint aDelta, mozilla::ScrollUnit aUnit, ScrollMode aMode,
+                nsIntPoint* aOverflow,
+                ScrollOrigin aOrigin = ScrollOrigin::NotSpecified,
+                nsIScrollableFrame::ScrollMomentum aMomentum =
+                    nsIScrollableFrame::NOT_MOMENTUM,
+                nsIScrollbarMediator::ScrollSnapMode aSnap =
+                    nsIScrollbarMediator::DISABLE_SNAP) final {
+    mHelper.ScrollBy(aDelta, aUnit, aMode, aOverflow, aOrigin, aMomentum,
+                     aSnap);
+  }
+  void ScrollByCSSPixels(const CSSIntPoint& aDelta,
+                         ScrollMode aMode = ScrollMode::Instant,
+                         ScrollOrigin aOrigin = ScrollOrigin::NotSpecified,
+                         nsIScrollbarMediator::ScrollSnapMode aSnap =
+                             nsIScrollbarMediator::DEFAULT) final {
+    mHelper.ScrollByCSSPixels(aDelta, aMode, aOrigin, aSnap);
+  }
+  void ScrollSnap() final { mHelper.ScrollSnap(); }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void ScrollToRestoredPosition() final { mHelper.ScrollToRestoredPosition(); }
+  void AddScrollPositionListener(nsIScrollPositionListener* aListener) final {
+    mHelper.AddScrollPositionListener(aListener);
+  }
+  void RemoveScrollPositionListener(
+      nsIScrollPositionListener* aListener) final {
+    mHelper.RemoveScrollPositionListener(aListener);
+  }
+  /**
+   * @note This method might destroy the frame, pres shell and other objects.
+   */
+  void CurPosAttributeChanged(nsIContent* aChild) final {
+    mHelper.CurPosAttributeChanged(aChild);
+  }
+  NS_IMETHOD PostScrolledAreaEventForCurrentArea() final {
+    mHelper.PostScrolledAreaEvent();
+    return NS_OK;
+  }
+  bool IsScrollingActive(nsDisplayListBuilder* aBuilder) final {
+    return mHelper.IsScrollingActive(aBuilder);
+  }
+  bool IsMaybeScrollingActive() const final {
+    return mHelper.IsMaybeScrollingActive();
+  }
+  bool IsMaybeAsynchronouslyScrolled() final {
+    return mHelper.IsMaybeAsynchronouslyScrolled();
+  }
+  void ResetScrollPositionForLayerPixelAlignment() final {
+    mHelper.ResetScrollPositionForLayerPixelAlignment();
+  }
+  bool DidHistoryRestore() const final { return mHelper.mDidHistoryRestore; }
+  void ClearDidHistoryRestore() final { mHelper.mDidHistoryRestore = false; }
+  void MarkEverScrolled() final { mHelper.MarkEverScrolled(); }
+  bool IsRectNearlyVisible(const nsRect& aRect) final {
+    return mHelper.IsRectNearlyVisible(aRect);
+  }
+  nsRect ExpandRectToNearlyVisible(const nsRect& aRect) const final {
+    return mHelper.ExpandRectToNearlyVisible(aRect);
+  }
+  ScrollOrigin LastScrollOrigin() final { return mHelper.LastScrollOrigin(); }
+  bool IsScrollAnimating(IncludeApzAnimation aIncludeApz) final {
+    return mHelper.IsScrollAnimating(aIncludeApz);
+  }
+  mozilla::ScrollGeneration CurrentScrollGeneration() const final {
+    return mHelper.CurrentScrollGeneration();
+  }
+  nsPoint LastScrollDestination() final {
+    return mHelper.LastScrollDestination();
+  }
+  nsTArray<mozilla::ScrollPositionUpdate> GetScrollUpdates() const final {
+    return mHelper.GetScrollUpdates();
+  }
+  bool HasScrollUpdates() const final { return mHelper.HasScrollUpdates(); }
+  void ResetScrollInfoIfNeeded(const mozilla::ScrollGeneration& aGeneration,
+                               bool aApzAnimationInProgress) final {
+    mHelper.ResetScrollInfoIfNeeded(aGeneration, aApzAnimationInProgress);
+  }
+  bool WantAsyncScroll() const final { return mHelper.WantAsyncScroll(); }
+  mozilla::Maybe<mozilla::layers::ScrollMetadata> ComputeScrollMetadata(
+      LayerManager* aLayerManager, const nsIFrame* aContainerReferenceFrame,
+      const Maybe<ContainerLayerParameters>& aParameters,
+      const mozilla::DisplayItemClip* aClip) const final {
+    return mHelper.ComputeScrollMetadata(
+        aLayerManager, aContainerReferenceFrame, aParameters, aClip);
+  }
+  void ClipLayerToDisplayPort(
+      Layer* aLayer, const mozilla::DisplayItemClip* aClip,
+      const ContainerLayerParameters& aParameters) const final {
+    mHelper.ClipLayerToDisplayPort(aLayer, aClip, aParameters);
+  }
+  void MarkScrollbarsDirtyForReflow() const final {
+    mHelper.MarkScrollbarsDirtyForReflow();
+  }
+  void UpdateScrollbarPosition() final { mHelper.UpdateScrollbarPosition(); }
+
+  // nsIStatefulFrame
+  mozilla::UniquePtr<mozilla::PresState> SaveState() final {
+    return mHelper.SaveState();
+  }
+  NS_IMETHOD RestoreState(mozilla::PresState* aState) final {
+    NS_ENSURE_ARG_POINTER(aState);
+    mHelper.RestoreState(aState);
+    return NS_OK;
+  }
+
+  bool IsFrameOfType(uint32_t aFlags) const final {
+    // Override bogus IsFrameOfType in nsBoxFrame.
+    if (aFlags & (nsIFrame::eReplacedContainsBlock | nsIFrame::eReplaced))
+      return false;
+    return nsBoxFrame::IsFrameOfType(aFlags);
+  }
+
+  void ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                    nsIScrollbarMediator::ScrollSnapMode aSnap =
+                        nsIScrollbarMediator::DISABLE_SNAP) final {
+    mHelper.ScrollByPage(aScrollbar, aDirection, aSnap);
+  }
+  void ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                     nsIScrollbarMediator::ScrollSnapMode aSnap =
+                         nsIScrollbarMediator::DISABLE_SNAP) final {
+    mHelper.ScrollByWhole(aScrollbar, aDirection, aSnap);
+  }
+  void ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                    nsIScrollbarMediator::ScrollSnapMode aSnap =
+                        nsIScrollbarMediator::DISABLE_SNAP) final {
+    mHelper.ScrollByLine(aScrollbar, aDirection, aSnap);
+  }
+  void RepeatButtonScroll(nsScrollbarFrame* aScrollbar) final {
+    mHelper.RepeatButtonScroll(aScrollbar);
+  }
+  void ThumbMoved(nsScrollbarFrame* aScrollbar, nscoord aOldPos,
+                  nscoord aNewPos) final {
+    mHelper.ThumbMoved(aScrollbar, aOldPos, aNewPos);
+  }
+  void ScrollbarReleased(nsScrollbarFrame* aScrollbar) final {
+    mHelper.ScrollbarReleased(aScrollbar);
+  }
+  void VisibilityChanged(bool aVisible) final {}
+  nsIFrame* GetScrollbarBox(bool aVertical) final {
+    return mHelper.GetScrollbarBox(aVertical);
+  }
+
+  void ScrollbarActivityStarted() const final;
+  void ScrollbarActivityStopped() const final;
+
+  bool IsScrollbarOnRight() const final { return mHelper.IsScrollbarOnRight(); }
+
+  bool ShouldSuppressScrollbarRepaints() const final {
+    return mHelper.ShouldSuppressScrollbarRepaints();
+  }
+
+  void SetTransformingByAPZ(bool aTransforming) final {
+    mHelper.SetTransformingByAPZ(aTransforming);
+  }
+  bool IsTransformingByAPZ() const final {
+    return mHelper.IsTransformingByAPZ();
+  }
+  void SetScrollableByAPZ(bool aScrollable) final {
+    mHelper.SetScrollableByAPZ(aScrollable);
+  }
+  void SetZoomableByAPZ(bool aZoomable) final {
+    mHelper.SetZoomableByAPZ(aZoomable);
+  }
+  void SetHasOutOfFlowContentInsideFilter() final {
+    mHelper.SetHasOutOfFlowContentInsideFilter();
+  }
+  bool DecideScrollableLayer(nsDisplayListBuilder* aBuilder,
+                             nsRect* aVisibleRect, nsRect* aDirtyRect,
+                             bool aSetBase) final {
+    return mHelper.DecideScrollableLayer(aBuilder, aVisibleRect, aDirtyRect,
+                                         aSetBase);
+  }
+  void NotifyApzTransaction() final { mHelper.NotifyApzTransaction(); }
+  void NotifyApproximateFrameVisibilityUpdate(bool aIgnoreDisplayPort) final {
+    mHelper.NotifyApproximateFrameVisibilityUpdate(aIgnoreDisplayPort);
+  }
+  bool GetDisplayPortAtLastApproximateFrameVisibilityUpdate(
+      nsRect* aDisplayPort) final {
+    return mHelper.GetDisplayPortAtLastApproximateFrameVisibilityUpdate(
+        aDisplayPort);
+  }
+  void TriggerDisplayPortExpiration() final {
+    mHelper.TriggerDisplayPortExpiration();
+  }
+
+  ScrollSnapInfo GetScrollSnapInfo() const final {
+    return mHelper.GetScrollSnapInfo(Nothing());
+  }
+
+  bool DragScroll(mozilla::WidgetEvent* aEvent) final {
+    return mHelper.DragScroll(aEvent);
+  }
+
+  void AsyncScrollbarDragInitiated(
+      uint64_t aDragBlockId,
+      mozilla::layers::ScrollDirection aDirection) final {
+    return mHelper.AsyncScrollbarDragInitiated(aDragBlockId, aDirection);
+  }
+
+  void AsyncScrollbarDragRejected() final {
+    return mHelper.AsyncScrollbarDragRejected();
+  }
+
+  bool IsRootScrollFrameOfDocument() const final {
+    return mHelper.IsRootScrollFrameOfDocument();
+  }
+
+  const ScrollAnchorContainer* Anchor() const final { return &mHelper.mAnchor; }
+
+  ScrollAnchorContainer* Anchor() final { return &mHelper.mAnchor; }
+
+  // Return the scrolled frame.
+  void AppendDirectlyOwnedAnonBoxes(nsTArray<OwnedAnonBox>& aResult) final {
+    aResult.AppendElement(OwnedAnonBox(mHelper.GetScrolledFrame()));
+  }
+
+  bool SmoothScrollVisual(
+      const nsPoint& aVisualViewportOffset,
+      mozilla::layers::FrameMetrics::ScrollOffsetUpdateType aUpdateType) final {
+    return mHelper.SmoothScrollVisual(aVisualViewportOffset, aUpdateType);
+  }
+
+  bool IsSmoothScroll(mozilla::dom::ScrollBehavior aBehavior) const final {
+    return mHelper.IsSmoothScroll(aBehavior);
+  }
+
+#ifdef DEBUG_FRAME_DUMP
+  nsresult GetFrameName(nsAString& aResult) const final;
+#endif
+
+ protected:
+  nsXULScrollFrame(ComputedStyle*, nsPresContext*, bool aIsRoot,
+                   bool aClipAllDescendants);
+
+  void ClampAndSetBounds(nsBoxLayoutState& aState, nsRect& aRect,
+                         nsPoint aScrollPosition,
+                         bool aRemoveOverflowAreas = false) {
+    /*
+     * For RTL frames, restore the original scrolled position of the right
+     * edge, then subtract the current width to find the physical position.
+     */
+    if (!mHelper.IsPhysicalLTR()) {
+      aRect.x = mHelper.mScrollPort.XMost() - aScrollPosition.x - aRect.width;
+    }
+    mHelper.mScrolledFrame->SetXULBounds(aState, aRect, aRemoveOverflowAreas);
+  }
+
+ private:
+  friend class mozilla::ScrollFrameHelper;
+  ScrollFrameHelper mHelper;
+};
+
+#endif /* nsGfxScrollFrame_h___ */