From 9e3c08db40b8916968b9f30096c7be3f00ce9647 Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Sun, 21 Apr 2024 13:44:51 +0200
Subject: Adding upstream version 1:115.7.0.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 gfx/layers/FrameMetrics.h | 1114 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 1114 insertions(+)
 create mode 100644 gfx/layers/FrameMetrics.h

(limited to 'gfx/layers/FrameMetrics.h')

diff --git a/gfx/layers/FrameMetrics.h b/gfx/layers/FrameMetrics.h
new file mode 100644
index 0000000000..fde4176f2a
--- /dev/null
+++ b/gfx/layers/FrameMetrics.h
@@ -0,0 +1,1114 @@
+/* -*- 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/. */
+
+#ifndef GFX_FRAMEMETRICS_H
+#define GFX_FRAMEMETRICS_H
+
+#include <stdint.h>  // for uint8_t, uint32_t, uint64_t
+#include <iosfwd>
+
+#include "Units.h"                  // for CSSRect, CSSPixel, etc
+#include "UnitTransforms.h"         // for ViewAs
+#include "mozilla/DefineEnum.h"     // for MOZ_DEFINE_ENUM
+#include "mozilla/HashFunctions.h"  // for HashGeneric
+#include "mozilla/Maybe.h"
+#include "mozilla/gfx/BasePoint.h"               // for BasePoint
+#include "mozilla/gfx/Rect.h"                    // for RoundedIn
+#include "mozilla/gfx/ScaleFactor.h"             // for ScaleFactor
+#include "mozilla/gfx/Logging.h"                 // for Log
+#include "mozilla/layers/LayersTypes.h"          // for ScrollDirection
+#include "mozilla/layers/ScrollableLayerGuid.h"  // for ScrollableLayerGuid
+#include "mozilla/ScrollPositionUpdate.h"        // for ScrollPositionUpdate
+#include "mozilla/ScrollSnapTargetId.h"
+#include "mozilla/StaticPtr.h"  // for StaticAutoPtr
+#include "mozilla/TimeStamp.h"  // for TimeStamp
+#include "nsTHashMap.h"         // for nsTHashMap
+#include "nsString.h"
+#include "PLDHashTable.h"  // for PLDHashNumber
+
+struct nsStyleDisplay;
+namespace mozilla {
+enum class StyleScrollSnapStop : uint8_t;
+enum class StyleScrollSnapStrictness : uint8_t;
+enum class StyleOverscrollBehavior : uint8_t;
+class WritingMode;
+}  // namespace mozilla
+
+namespace IPC {
+template <typename T>
+struct ParamTraits;
+}  // namespace IPC
+
+namespace mozilla {
+namespace layers {
+
+/**
+ * Metrics about a scroll frame that are sent to the compositor and used
+ * by APZ.
+ *
+ * This is used for two main purposes:
+ *
+ *   (1) Sending information about a scroll frame to the compositor and APZ
+ *       as part of a layers or WebRender transaction.
+ *   (2) Storing information about a scroll frame in APZ that persists
+ *       between transactions.
+ *
+ * TODO: Separate these two uses into two distinct structures.
+ *
+ * A related class, RepaintRequest, is used for sending information about a
+ * scroll frame back from the compositor to the main thread when requesting
+ * a repaint of the scroll frame's contents.
+ */
+struct FrameMetrics {
+  friend struct IPC::ParamTraits<mozilla::layers::FrameMetrics>;
+  friend std::ostream& operator<<(std::ostream& aStream,
+                                  const FrameMetrics& aMetrics);
+
+  typedef ScrollableLayerGuid::ViewID ViewID;
+
+ public:
+  // clang-format off
+  MOZ_DEFINE_ENUM_WITH_BASE_AT_CLASS_SCOPE(
+    ScrollOffsetUpdateType, uint8_t, (
+      eNone,          // The default; the scroll offset was not updated
+      eMainThread,    // The scroll offset was updated by the main thread.
+      eRestore        // The scroll offset was updated by the main thread, but
+                      // as a restore from history or after a frame
+                      // reconstruction.  In this case, APZ can ignore the
+                      // offset change if the user has done an APZ scroll
+                      // already.
+  ));
+  // clang-format on
+
+  FrameMetrics()
+      : mScrollId(ScrollableLayerGuid::NULL_SCROLL_ID),
+        mPresShellResolution(1),
+        mCompositionBounds(0, 0, 0, 0),
+        mCompositionBoundsWidthIgnoringScrollbars(0),
+        mDisplayPort(0, 0, 0, 0),
+        mScrollableRect(0, 0, 0, 0),
+        mCumulativeResolution(),
+        mDevPixelsPerCSSPixel(1),
+        mScrollOffset(0, 0),
+        mZoom(),
+        mBoundingCompositionSize(0, 0),
+        mPresShellId(-1),
+        mLayoutViewport(0, 0, 0, 0),
+        mTransformToAncestorScale(),
+        mPaintRequestTime(),
+        mVisualDestination(0, 0),
+        mVisualScrollUpdateType(eNone),
+        mCompositionSizeWithoutDynamicToolbar(),
+        mIsRootContent(false),
+        mIsScrollInfoLayer(false),
+        mHasNonZeroDisplayPortMargins(false),
+        mMinimalDisplayPort(false) {}
+
+  // Default copy ctor and operator= are fine
+
+  bool operator==(const FrameMetrics& aOther) const {
+    // Put mScrollId at the top since it's the most likely one to fail.
+    return mScrollId == aOther.mScrollId &&
+           mPresShellResolution == aOther.mPresShellResolution &&
+           mCompositionBounds.IsEqualEdges(aOther.mCompositionBounds) &&
+           mCompositionBoundsWidthIgnoringScrollbars ==
+               aOther.mCompositionBoundsWidthIgnoringScrollbars &&
+           mDisplayPort.IsEqualEdges(aOther.mDisplayPort) &&
+           mScrollableRect.IsEqualEdges(aOther.mScrollableRect) &&
+           mCumulativeResolution == aOther.mCumulativeResolution &&
+           mDevPixelsPerCSSPixel == aOther.mDevPixelsPerCSSPixel &&
+           mScrollOffset == aOther.mScrollOffset &&
+           // don't compare mZoom
+           mScrollGeneration == aOther.mScrollGeneration &&
+           mBoundingCompositionSize == aOther.mBoundingCompositionSize &&
+           mPresShellId == aOther.mPresShellId &&
+           mLayoutViewport.IsEqualEdges(aOther.mLayoutViewport) &&
+           mTransformToAncestorScale == aOther.mTransformToAncestorScale &&
+           mPaintRequestTime == aOther.mPaintRequestTime &&
+           mVisualDestination == aOther.mVisualDestination &&
+           mVisualScrollUpdateType == aOther.mVisualScrollUpdateType &&
+           mIsRootContent == aOther.mIsRootContent &&
+           mIsScrollInfoLayer == aOther.mIsScrollInfoLayer &&
+           mHasNonZeroDisplayPortMargins ==
+               aOther.mHasNonZeroDisplayPortMargins &&
+           mMinimalDisplayPort == aOther.mMinimalDisplayPort &&
+           mFixedLayerMargins == aOther.mFixedLayerMargins &&
+           mCompositionSizeWithoutDynamicToolbar ==
+               aOther.mCompositionSizeWithoutDynamicToolbar;
+  }
+
+  bool operator!=(const FrameMetrics& aOther) const {
+    return !operator==(aOther);
+  }
+
+  bool IsScrollable() const {
+    return mScrollId != ScrollableLayerGuid::NULL_SCROLL_ID;
+  }
+
+  CSSToScreenScale2D DisplayportPixelsPerCSSPixel() const {
+    // Note: mZoom includes the async zoom. We want to include the async zoom
+    // even though the size of the pixels of our *current* displayport does not
+    // yet reflect it, because this function is used in the context of a repaint
+    // request where we'll be asking for a *new* displayport which does reflect
+    // the async zoom. Note 2: we include the transform to ancestor scale
+    // because this function (as the name implies) is used only in various
+    // displayport calculation related places, and those calculations want the
+    // transform to ancestor scale to be included becaese they want to reason
+    // about pixels which are the same size as screen pixels (so displayport
+    // sizes are e.g. limited to a multiple of the screen size). Whereas mZoom
+    // and mCumulativeResolution do not include it because of expectations of
+    // the code where they are used.
+    return mZoom * mTransformToAncestorScale;
+  }
+
+  CSSToLayerScale LayersPixelsPerCSSPixel() const {
+    return mDevPixelsPerCSSPixel * mCumulativeResolution;
+  }
+
+  // Get the amount by which this frame has been zoomed since the last repaint.
+  LayerToParentLayerScale GetAsyncZoom() const {
+    return mZoom / LayersPixelsPerCSSPixel();
+  }
+
+  // Ensure the scrollableRect is at least as big as the compositionBounds
+  // because the scrollableRect can be smaller if the content is not large
+  // and the scrollableRect hasn't been updated yet.
+  // We move the scrollableRect up because we don't know if we can move it
+  // down. i.e. we know that scrollableRect can go back as far as zero.
+  // but we don't know how much further ahead it can go.
+  CSSRect GetExpandedScrollableRect() const {
+    CSSRect scrollableRect = mScrollableRect;
+    CSSSize compSize = CalculateCompositedSizeInCssPixels();
+    if (scrollableRect.Width() < compSize.width) {
+      scrollableRect.SetRectX(
+          std::max(0.f, scrollableRect.X() -
+                            (compSize.width - scrollableRect.Width())),
+          compSize.width);
+    }
+
+    if (scrollableRect.Height() < compSize.height) {
+      scrollableRect.SetRectY(
+          std::max(0.f, scrollableRect.Y() -
+                            (compSize.height - scrollableRect.Height())),
+          compSize.height);
+    }
+
+    return scrollableRect;
+  }
+
+  CSSSize CalculateCompositedSizeInCssPixels() const {
+    return CalculateCompositedSizeInCssPixels(mCompositionBounds, mZoom);
+  }
+
+  /*
+   * Calculate the composition bounds of this frame in the CSS pixels of
+   * the content surrounding the scroll frame (OuterCSS pixels).
+   * Note that it does not make sense to ask for the composition bounds in the
+   * CSS pixels of the scrolled content (that is, regular CSS pixels),
+   * because the origin of the composition bounds is not meaningful in that
+   * coordinate space. (The size is, use CalculateCompositedSizeInCssPixels()
+   * for that.)
+   */
+  OuterCSSRect CalculateCompositionBoundsInOuterCssPixels() const {
+    if (GetZoom() == CSSToParentLayerScale(0)) {
+      return OuterCSSRect();  // avoid division by zero
+    }
+    // The CSS pixels of the scrolled content and the CSS pixels of the
+    // surrounding content only differ if the scrolled content is rendered
+    // at a higher resolution, and the difference is the resolution.
+    return mCompositionBounds / GetZoom() * GetCSSToOuterCSSScale();
+  }
+
+  CSSSize CalculateBoundedCompositedSizeInCssPixels() const {
+    CSSSize size = CalculateCompositedSizeInCssPixels();
+    size.width = std::min(size.width, mBoundingCompositionSize.width);
+    size.height = std::min(size.height, mBoundingCompositionSize.height);
+    return size;
+  }
+
+  CSSRect CalculateScrollRange() const {
+    return CalculateScrollRange(mScrollableRect, mCompositionBounds, mZoom);
+  }
+
+  void ScrollBy(const CSSPoint& aPoint) {
+    SetVisualScrollOffset(GetVisualScrollOffset() + aPoint);
+  }
+
+  void ZoomBy(float aScale) { mZoom.scale *= aScale; }
+
+  /*
+   * Compares an APZ frame metrics with an incoming content frame metrics
+   * to see if APZ has a scroll offset that has not been incorporated into
+   * the content frame metrics.
+   */
+  bool HasPendingScroll(const FrameMetrics& aContentFrameMetrics) const {
+    return GetVisualScrollOffset() !=
+           aContentFrameMetrics.GetVisualScrollOffset();
+  }
+
+  /*
+   * Returns true if the layout scroll offset or visual scroll offset changed.
+   */
+  bool ApplyScrollUpdateFrom(const ScrollPositionUpdate& aUpdate);
+
+  /**
+   * Applies the relative scroll offset update contained in aOther to the
+   * scroll offset contained in this. The scroll delta is clamped to the
+   * scrollable region.
+   *
+   * @returns The clamped scroll offset delta that was applied
+   */
+  CSSPoint ApplyRelativeScrollUpdateFrom(const ScrollPositionUpdate& aUpdate);
+
+  CSSPoint ApplyPureRelativeScrollUpdateFrom(
+      const ScrollPositionUpdate& aUpdate);
+
+  void UpdatePendingScrollInfo(const ScrollPositionUpdate& aInfo);
+
+ public:
+  void SetPresShellResolution(float aPresShellResolution) {
+    mPresShellResolution = aPresShellResolution;
+  }
+
+  float GetPresShellResolution() const { return mPresShellResolution; }
+
+  void SetCompositionBounds(const ParentLayerRect& aCompositionBounds) {
+    mCompositionBounds = aCompositionBounds;
+  }
+
+  const ParentLayerRect& GetCompositionBounds() const {
+    return mCompositionBounds;
+  }
+
+  void SetCompositionBoundsWidthIgnoringScrollbars(
+      const ParentLayerCoord aCompositionBoundsWidthIgnoringScrollbars) {
+    mCompositionBoundsWidthIgnoringScrollbars =
+        aCompositionBoundsWidthIgnoringScrollbars;
+  }
+
+  const ParentLayerCoord GetCompositionBoundsWidthIgnoringScrollbars() const {
+    return mCompositionBoundsWidthIgnoringScrollbars;
+  }
+
+  void SetDisplayPort(const CSSRect& aDisplayPort) {
+    mDisplayPort = aDisplayPort;
+  }
+
+  const CSSRect& GetDisplayPort() const { return mDisplayPort; }
+
+  void SetCumulativeResolution(
+      const LayoutDeviceToLayerScale& aCumulativeResolution) {
+    mCumulativeResolution = aCumulativeResolution;
+  }
+
+  const LayoutDeviceToLayerScale& GetCumulativeResolution() const {
+    return mCumulativeResolution;
+  }
+
+  void SetDevPixelsPerCSSPixel(
+      const CSSToLayoutDeviceScale& aDevPixelsPerCSSPixel) {
+    mDevPixelsPerCSSPixel = aDevPixelsPerCSSPixel;
+  }
+
+  const CSSToLayoutDeviceScale& GetDevPixelsPerCSSPixel() const {
+    return mDevPixelsPerCSSPixel;
+  }
+
+  CSSToOuterCSSScale GetCSSToOuterCSSScale() const {
+    // The scale difference between CSS and OuterCSS pixels is the
+    // part of the zoom that's not subject to all enclosing content,
+    // i.e. the pres shell resolution.
+    return CSSToOuterCSSScale(mPresShellResolution);
+  }
+
+  void SetIsRootContent(bool aIsRootContent) {
+    mIsRootContent = aIsRootContent;
+  }
+
+  bool IsRootContent() const { return mIsRootContent; }
+
+  // Set scroll offset, first clamping to the scroll range.
+  // Return true if it changed.
+  bool ClampAndSetVisualScrollOffset(const CSSPoint& aScrollOffset) {
+    CSSPoint offsetBefore = GetVisualScrollOffset();
+    SetVisualScrollOffset(CalculateScrollRange().ClampPoint(aScrollOffset));
+    return (offsetBefore != GetVisualScrollOffset());
+  }
+
+  CSSPoint GetLayoutScrollOffset() const { return mLayoutViewport.TopLeft(); }
+  // Returns true if it changed.
+  bool SetLayoutScrollOffset(const CSSPoint& aLayoutScrollOffset) {
+    CSSPoint offsetBefore = GetLayoutScrollOffset();
+    mLayoutViewport.MoveTo(aLayoutScrollOffset);
+    return (offsetBefore != GetLayoutScrollOffset());
+  }
+
+  const CSSPoint& GetVisualScrollOffset() const { return mScrollOffset; }
+  void SetVisualScrollOffset(const CSSPoint& aVisualScrollOffset) {
+    mScrollOffset = aVisualScrollOffset;
+  }
+
+  void SetZoom(const CSSToParentLayerScale& aZoom) { mZoom = aZoom; }
+
+  const CSSToParentLayerScale& GetZoom() const { return mZoom; }
+
+  void SetScrollGeneration(
+      const MainThreadScrollGeneration& aScrollGeneration) {
+    mScrollGeneration = aScrollGeneration;
+  }
+
+  MainThreadScrollGeneration GetScrollGeneration() const {
+    return mScrollGeneration;
+  }
+
+  ViewID GetScrollId() const { return mScrollId; }
+
+  void SetScrollId(ViewID scrollId) { mScrollId = scrollId; }
+
+  void SetBoundingCompositionSize(const CSSSize& aBoundingCompositionSize) {
+    mBoundingCompositionSize = aBoundingCompositionSize;
+  }
+
+  const CSSSize& GetBoundingCompositionSize() const {
+    return mBoundingCompositionSize;
+  }
+
+  uint32_t GetPresShellId() const { return mPresShellId; }
+
+  void SetPresShellId(uint32_t aPresShellId) { mPresShellId = aPresShellId; }
+
+  void SetLayoutViewport(const CSSRect& aLayoutViewport) {
+    mLayoutViewport = aLayoutViewport;
+  }
+
+  const CSSRect& GetLayoutViewport() const { return mLayoutViewport; }
+
+  CSSRect GetVisualViewport() const {
+    return CSSRect(GetVisualScrollOffset(),
+                   CalculateCompositedSizeInCssPixels());
+  }
+
+  void SetTransformToAncestorScale(
+      const ParentLayerToScreenScale2D& aTransformToAncestorScale) {
+    mTransformToAncestorScale = aTransformToAncestorScale;
+  }
+
+  const ParentLayerToScreenScale2D& GetTransformToAncestorScale() const {
+    return mTransformToAncestorScale;
+  }
+
+  const CSSRect& GetScrollableRect() const { return mScrollableRect; }
+
+  void SetScrollableRect(const CSSRect& aScrollableRect) {
+    mScrollableRect = aScrollableRect;
+  }
+
+  // If the frame is in vertical-RTL writing mode(E.g. "writing-mode:
+  // vertical-rl" in CSS), or if it's in horizontal-RTL writing-mode(E.g.
+  // "writing-mode: horizontal-tb; direction: rtl;" in CSS), then this function
+  // returns true. From the representation perspective, frames whose horizontal
+  // contents start at rightside also cause their horizontal scrollbars, if any,
+  // initially start at rightside. So we can also learn about the initial side
+  // of the horizontal scrollbar for the frame by calling this function.
+  bool IsHorizontalContentRightToLeft() const { return mScrollableRect.x < 0; }
+
+  void SetPaintRequestTime(const TimeStamp& aTime) {
+    mPaintRequestTime = aTime;
+  }
+  const TimeStamp& GetPaintRequestTime() const { return mPaintRequestTime; }
+
+  void SetIsScrollInfoLayer(bool aIsScrollInfoLayer) {
+    mIsScrollInfoLayer = aIsScrollInfoLayer;
+  }
+  bool IsScrollInfoLayer() const { return mIsScrollInfoLayer; }
+
+  void SetHasNonZeroDisplayPortMargins(bool aHasNonZeroDisplayPortMargins) {
+    mHasNonZeroDisplayPortMargins = aHasNonZeroDisplayPortMargins;
+  }
+  bool HasNonZeroDisplayPortMargins() const {
+    return mHasNonZeroDisplayPortMargins;
+  }
+
+  void SetMinimalDisplayPort(bool aMinimalDisplayPort) {
+    mMinimalDisplayPort = aMinimalDisplayPort;
+  }
+  bool IsMinimalDisplayPort() const { return mMinimalDisplayPort; }
+
+  void SetVisualDestination(const CSSPoint& aVisualDestination) {
+    mVisualDestination = aVisualDestination;
+  }
+  const CSSPoint& GetVisualDestination() const { return mVisualDestination; }
+
+  void SetVisualScrollUpdateType(ScrollOffsetUpdateType aUpdateType) {
+    mVisualScrollUpdateType = aUpdateType;
+  }
+  ScrollOffsetUpdateType GetVisualScrollUpdateType() const {
+    return mVisualScrollUpdateType;
+  }
+
+  // Determine if the visual viewport is outside of the layout viewport and
+  // adjust the x,y-offset in mLayoutViewport accordingly. This is necessary to
+  // allow APZ to async-scroll the layout viewport.
+  //
+  // This is a no-op if mIsRootContent is false.
+  void RecalculateLayoutViewportOffset();
+
+  void SetFixedLayerMargins(const ScreenMargin& aFixedLayerMargins) {
+    mFixedLayerMargins = aFixedLayerMargins;
+  }
+  const ScreenMargin& GetFixedLayerMargins() const {
+    return mFixedLayerMargins;
+  }
+
+  void SetCompositionSizeWithoutDynamicToolbar(const ParentLayerSize& aSize) {
+    MOZ_ASSERT(mIsRootContent);
+    mCompositionSizeWithoutDynamicToolbar = aSize;
+  }
+  const ParentLayerSize& GetCompositionSizeWithoutDynamicToolbar() const {
+    MOZ_ASSERT(mIsRootContent);
+    return mCompositionSizeWithoutDynamicToolbar;
+  }
+
+  // Helper function for RecalculateViewportOffset(). Exposed so that
+  // APZC can perform the operation on other copies of the layout
+  // and visual viewport rects (e.g. the "effective" ones used to implement
+  // the frame delay).
+  // Modifies |aLayoutViewport| to continue enclosing |aVisualViewport|
+  // if possible.
+  // The layout viewport needs to remain clamped to the scrollable rect,
+  // and we pass in the scrollable rect so this function can maintain that
+  // constraint.
+  static void KeepLayoutViewportEnclosingVisualViewport(
+      const CSSRect& aVisualViewport, const CSSRect& aScrollableRect,
+      CSSRect& aLayoutViewport);
+
+  // Helper functions exposed so we can perform operations on copies outside of
+  // frame metrics object.
+  static CSSRect CalculateScrollRange(const CSSRect& aScrollableRect,
+                                      const ParentLayerRect& aCompositionBounds,
+                                      const CSSToParentLayerScale& aZoom);
+  static CSSSize CalculateCompositedSizeInCssPixels(
+      const ParentLayerRect& aCompositionBounds,
+      const CSSToParentLayerScale& aZoom);
+
+ private:
+  // A ID assigned to each scrollable frame, unique within each LayersId..
+  ViewID mScrollId;
+
+  // The pres-shell resolution that has been induced on the document containing
+  // this scroll frame as a result of zooming this scroll frame (whether via
+  // user action, or choosing an initial zoom level on page load). This can
+  // only be different from 1.0 for frames that are zoomable, which currently
+  // is just the root content document's root scroll frame
+  // (mIsRootContent = true).
+  // This is a plain float rather than a ScaleFactor because in and of itself
+  // it does not convert between any coordinate spaces for which we have names.
+  float mPresShellResolution;
+
+  // This is the area within the widget that we're compositing to. It is in the
+  // layer coordinates of the scrollable content's parent layer.
+  //
+  // The size of the composition bounds corresponds to the size of the scroll
+  // frame's scroll port (but in a coordinate system where the size does not
+  // change during zooming).
+  //
+  // The origin of the composition bounds is relative to the scroll node origin.
+  // (The "scroll node origin" is the point such that applying the APZC's
+  //  apzc-to-screen transform to it takes you to the window origin, which is
+  //  what Screen event coordinates are relative to. In layout terms, it's
+  //  the origin of the reference frame passed to ComputeScrollMetadata().)
+  // Unlike the scroll port's origin, it does not change during scrolling of
+  // the scrollable layer to which it is associated. However, it may change due
+  // to scrolling of ancestor layers.
+  //
+  // This value is provided by Gecko at layout/paint time.
+  ParentLayerRect mCompositionBounds;
+
+  // For RCD-RSF this is the width of the composition bounds ignoring
+  // scrollbars. For everything else this will be the same as the width of the
+  // composition bounds. Only needed for the "resolution changed" check in
+  // NotifyLayersUpdated, once that switches to using IsResolutionUpdated we can
+  // remove this.
+  ParentLayerCoord mCompositionBoundsWidthIgnoringScrollbars;
+
+  // The area of a scroll frame's contents that has been painted, relative to
+  // GetLayoutScrollOffset().
+  //
+  // Should not be larger than GetExpandedScrollableRect().
+  //
+  // To pre-render a margin of 100 CSS pixels around the scroll port,
+  // { x = -100, y = - 100,
+  //   width = scrollPort.width + 200, height = scrollPort.height + 200 }
+  // where scrollPort = CalculateCompositedSizeInCssPixels().
+  CSSRect mDisplayPort;
+
+  // The scrollable bounds of a frame. This is determined by reflow.
+  // Ordinarily the x and y will be 0 and the width and height will be the
+  // size of the element being scrolled. However for RTL pages or elements
+  // the x value may be negative.
+  //
+  // For scrollable frames that are overflow:hidden the x and y are usually
+  // set to the value of the current scroll offset, and the width and height
+  // will match the composition bounds width and height. In effect this reduces
+  // the scrollable range to 0.
+  //
+  // This is in the same coordinate space as |mScrollOffset|, but a different
+  // coordinate space than |mDisplayPort|. Note also that this coordinate
+  // system is understood by window.scrollTo().
+  CSSRect mScrollableRect;
+
+  // The cumulative resolution of the current frame. This is the product of the
+  // pres-shell resolutions of the document containing this scroll frame and its
+  // in-process ancestors. This information is provided by Gecko at layout/paint
+  // time. Notably, for out of process iframes cumulative resolution will be 1.
+  // The reason for this is that AsyncPanZoomController::GetTransformToThis does
+  // not contain the resolution in the process of the root content document, but
+  // in oop iframes AsyncPanZoomController::GetTransformToThis does contain the
+  // resolution. This makes coordinate math work out in APZ code because in the
+  // old layers backend GetTransformToThis was a transform of rendered pixels,
+  // and the pixels were rendered with the scale applied already. The reason
+  // that AsyncPanZoomController::GetTransformToThis contains the scale in oop
+  // iframes is because we include the resolution in the transform that includes
+  // the iframe via this call
+  // https://searchfox.org/mozilla-central/rev/2eebd6e256fa0355e08421265e57ee1307836d92/layout/generic/nsSubDocumentFrame.cpp#1404
+  // So when coordinates are passed to the process of the oop iframe they have
+  // the resolution removed by unapplying that transform which includes the
+  // resolution.
+  LayoutDeviceToLayerScale mCumulativeResolution;
+
+  // The conversion factor between CSS pixels and device pixels for this frame.
+  // This can vary based on a variety of things, such as reflowing-zoom.
+  CSSToLayoutDeviceScale mDevPixelsPerCSSPixel;
+
+  // The position of the top-left of the scroll frame's scroll port, relative
+  // to the scrollable content's origin.
+  //
+  // This is in the same coordinate space as |mScrollableRect|, but a different
+  // coordinate space than |mDisplayPort|.
+  //
+  // It is required that the rect:
+  // { x = mScrollOffset.x, y = mScrollOffset.y,
+  //   width = scrollPort.width,
+  //   height = scrollPort.height }
+  // (where scrollPort = CalculateCompositedSizeInCssPixels())
+  // be within |mScrollableRect|.
+  CSSPoint mScrollOffset;
+
+  // The "user zoom". Content is painted by gecko at mCumulativeResolution *
+  // mDevPixelsPerCSSPixel, but will be drawn to the screen at mZoom. In the
+  // steady state, the two will be the same, but during an async zoom action the
+  // two may diverge. This information is initialized in Gecko but updated in
+  // the APZC.
+  CSSToParentLayerScale mZoom;
+
+  // The scroll generation counter used to acknowledge the scroll offset update.
+  MainThreadScrollGeneration mScrollGeneration;
+
+  // A bounding size for our composition bounds (no larger than the
+  // cross-process RCD-RSF's composition size), in local CSS pixels.
+  CSSSize mBoundingCompositionSize;
+
+  uint32_t mPresShellId;
+
+  // For a root scroll frame (RSF), the document's layout viewport
+  // (sometimes called "CSS viewport" in older code).
+  //
+  // Its size is the dimensions we're using to constrain the <html> element
+  // of the document (i.e. the initial containing block (ICB) size).
+  //
+  // Its origin is the RSF's layout scroll position, i.e. the scroll position
+  // exposed to web content via window.scrollX/Y.
+  //
+  // Note that only the root content document's RSF has a layout viewport
+  // that's distinct from the visual viewport. For an iframe RSF, the two
+  // are the same.
+  //
+  // For a scroll frame that is not an RSF, this metric is meaningless and
+  // invalid.
+  CSSRect mLayoutViewport;
+
+  // The scale induced by css transforms and presshell resolution in this
+  // process and any ancestor processes that encloses this scroll frame that is
+  // _not_ included in mCumulativeResolution. This means that in the process of
+  // the root content document this only includes css transform scale (which
+  // happens in that process, but we assume there can be no css transform scale
+  // above the root content document). In other processes it includes css
+  // transform scale and any resolution scale in the current process and all
+  // ancestor processes.
+  ParentLayerToScreenScale2D mTransformToAncestorScale;
+
+  // The time at which the APZC last requested a repaint for this scroll frame.
+  TimeStamp mPaintRequestTime;
+
+  // These fields are used when the main thread wants to set a visual viewport
+  // offset that's distinct from the layout viewport offset.
+  // In this case, mVisualScrollUpdateType is set to eMainThread, and
+  // mVisualDestination is set to desired visual destination (relative
+  // to the document, like mScrollOffset).
+  CSSPoint mVisualDestination;
+  ScrollOffsetUpdateType mVisualScrollUpdateType;
+
+  // 'fixed layer margins' on the main-thread. This is only used for the
+  // root-content scroll frame.
+  ScreenMargin mFixedLayerMargins;
+
+  // Similar to mCompositionBounds.Size() but not including the dynamic toolbar
+  // height.
+  // If we are not using a dynamic toolbar, this has the same value as
+  // mCompositionBounds.Size().
+  ParentLayerSize mCompositionSizeWithoutDynamicToolbar;
+
+  // Whether or not this is the root scroll frame for the root content document.
+  bool mIsRootContent : 1;
+
+  // True if this scroll frame is a scroll info layer. A scroll info layer is
+  // not layerized and its content cannot be truly async-scrolled, but its
+  // metrics are still sent to and updated by the compositor, with the updates
+  // being reflected on the next paint rather than the next composite.
+  bool mIsScrollInfoLayer : 1;
+
+  // Whether there are non-zero display port margins set on this element.
+  bool mHasNonZeroDisplayPortMargins : 1;
+
+  // Whether this scroll frame is using a minimal display port, which means that
+  // any set display port margins are ignored when calculating the display port
+  // and instead zero margins are used and further no tile or alignment
+  // boundaries are used that could potentially expand the size.
+  bool mMinimalDisplayPort : 1;
+
+  // WARNING!!!!
+  //
+  // When adding a new field:
+  //
+  //  - First, consider whether the field can be added to ScrollMetadata
+  //    instead. If so, prefer that.
+  //
+  //  - Otherwise, the following places should be updated to include them
+  //    (as needed):
+  //      FrameMetrics::operator ==
+  //      AsyncPanZoomController::NotifyLayersUpdated
+  //      The ParamTraits specialization in LayersMessageUtils.h
+  //
+  // Please add new fields above this comment.
+};
+
+struct ScrollSnapInfo {
+  ScrollSnapInfo();
+
+  bool operator==(const ScrollSnapInfo& aOther) const {
+    return mScrollSnapStrictnessX == aOther.mScrollSnapStrictnessX &&
+           mScrollSnapStrictnessY == aOther.mScrollSnapStrictnessY &&
+           mSnapTargets == aOther.mSnapTargets &&
+           mXRangeWiderThanSnapport == aOther.mXRangeWiderThanSnapport &&
+           mYRangeWiderThanSnapport == aOther.mYRangeWiderThanSnapport &&
+           mSnapportSize == aOther.mSnapportSize;
+  }
+
+  bool HasScrollSnapping() const;
+  bool HasSnapPositions() const;
+
+  void InitializeScrollSnapStrictness(WritingMode aWritingMode,
+                                      const nsStyleDisplay* aDisplay);
+
+  // The scroll frame's scroll-snap-type.
+  StyleScrollSnapStrictness mScrollSnapStrictnessX;
+  StyleScrollSnapStrictness mScrollSnapStrictnessY;
+
+  struct SnapTarget {
+    // The scroll positions corresponding to scroll-snap-align values.
+    Maybe<nscoord> mSnapPositionX;
+    Maybe<nscoord> mSnapPositionY;
+
+    // https://drafts.csswg.org/css-scroll-snap/#scroll-snap-area
+    nsRect mSnapArea;
+
+    // https://drafts.csswg.org/css-scroll-snap/#propdef-scroll-snap-stop
+    StyleScrollSnapStop mScrollSnapStop;
+
+    // Use for tracking the last snapped target.
+    ScrollSnapTargetId mTargetId;
+
+    SnapTarget() = default;
+
+    SnapTarget(Maybe<nscoord>&& aSnapPositionX, Maybe<nscoord>&& aSnapPositionY,
+               nsRect&& aSnapArea, StyleScrollSnapStop aScrollSnapStop,
+               ScrollSnapTargetId aTargetId)
+        : mSnapPositionX(std::move(aSnapPositionX)),
+          mSnapPositionY(std::move(aSnapPositionY)),
+          mSnapArea(std::move(aSnapArea)),
+          mScrollSnapStop(aScrollSnapStop),
+          mTargetId(aTargetId) {}
+
+    bool operator==(const SnapTarget& aOther) const {
+      return mSnapPositionX == aOther.mSnapPositionX &&
+             mSnapPositionY == aOther.mSnapPositionY &&
+             mSnapArea == aOther.mSnapArea &&
+             mScrollSnapStop == aOther.mScrollSnapStop &&
+             mTargetId == aOther.mTargetId;
+    }
+    bool IsValidFor(const nsPoint& aDestination,
+                    const nsSize aSnapportSize) const {
+      nsPoint snapPoint(mSnapPositionX ? *mSnapPositionX : aDestination.x,
+                        mSnapPositionY ? *mSnapPositionY : aDestination.y);
+      nsRect snappedPort = nsRect(snapPoint, aSnapportSize);
+      // Ignore snap points if snapping to the point would leave the snap area
+      // outside of the snapport.
+      // https://drafts.csswg.org/css-scroll-snap-1/#snap-scope
+      return snappedPort.Intersects(mSnapArea);
+    }
+  };
+
+  CopyableTArray<SnapTarget> mSnapTargets;
+
+  struct ScrollSnapRange {
+    ScrollSnapRange() = default;
+
+    ScrollSnapRange(nscoord aStart, nscoord aEnd, ScrollSnapTargetId aTargetId)
+        : mStart(aStart), mEnd(aEnd), mTargetId(aTargetId) {}
+
+    nscoord mStart;
+    nscoord mEnd;
+    ScrollSnapTargetId mTargetId;
+
+    bool operator==(const ScrollSnapRange& aOther) const {
+      return mStart == aOther.mStart && mEnd == aOther.mEnd &&
+             mTargetId == aOther.mTargetId;
+    }
+
+    // Returns true if |aPoint| is a valid snap position in this range.
+    bool IsValid(nscoord aPoint, nscoord aSnapportSize) const {
+      MOZ_ASSERT(mEnd - mStart > aSnapportSize);
+      return mStart <= aPoint && aPoint <= mEnd - aSnapportSize;
+    }
+  };
+  // An array of the range that the target element is larger than the snapport
+  // on the axis.
+  // Snap positions in this range will be valid snap positions in the case where
+  // the distance between the closest snap position and the second closest snap
+  // position is still larger than the snapport size.
+  // See https://drafts.csswg.org/css-scroll-snap-1/#snap-overflow
+  //
+  // Note: This range contains scroll-margin values.
+  CopyableTArray<ScrollSnapRange> mXRangeWiderThanSnapport;
+  CopyableTArray<ScrollSnapRange> mYRangeWiderThanSnapport;
+
+  // Note: This snapport size has been already deflated by scroll-padding.
+  nsSize mSnapportSize;
+};
+
+// clang-format off
+MOZ_DEFINE_ENUM_CLASS_WITH_BASE(
+  OverscrollBehavior, uint8_t, (
+    Auto,
+    Contain,
+    None
+));
+// clang-format on
+
+std::ostream& operator<<(std::ostream& aStream,
+                         const OverscrollBehavior& aBehavior);
+
+struct OverscrollBehaviorInfo {
+  OverscrollBehaviorInfo();
+
+  // Construct from StyleOverscrollBehavior values.
+  static OverscrollBehaviorInfo FromStyleConstants(
+      StyleOverscrollBehavior aBehaviorX, StyleOverscrollBehavior aBehaviorY);
+
+  bool operator==(const OverscrollBehaviorInfo& aOther) const;
+  friend std::ostream& operator<<(std::ostream& aStream,
+                                  const OverscrollBehaviorInfo& aInfo);
+
+  OverscrollBehavior mBehaviorX;
+  OverscrollBehavior mBehaviorY;
+};
+
+/**
+ * Metadata about a scroll frame that's sent to the compositor during a layers
+ * or WebRender transaction, and also stored by APZ between transactions.
+ * This includes the scroll frame's FrameMetrics, as well as other metadata.
+ * We don't put the other metadata into FrameMetrics to avoid FrameMetrics
+ * becoming too bloated (as a FrameMetrics is e.g. stored in memory shared
+ * with the content process).
+ */
+struct ScrollMetadata {
+  friend struct IPC::ParamTraits<mozilla::layers::ScrollMetadata>;
+  friend std::ostream& operator<<(std::ostream& aStream,
+                                  const ScrollMetadata& aMetadata);
+
+  typedef ScrollableLayerGuid::ViewID ViewID;
+
+ public:
+  static StaticAutoPtr<const ScrollMetadata>
+      sNullMetadata;  // We sometimes need an empty metadata
+
+  ScrollMetadata()
+      : mMetrics(),
+        mSnapInfo(),
+        mScrollParentId(ScrollableLayerGuid::NULL_SCROLL_ID),
+        mContentDescription(),
+        mLineScrollAmount(0, 0),
+        mPageScrollAmount(0, 0),
+        mHasScrollgrab(false),
+        mIsLayersIdRoot(false),
+        mIsAutoDirRootContentRTL(false),
+        mForceDisableApz(false),
+        mResolutionUpdated(false),
+        mIsRDMTouchSimulationActive(false),
+        mDidContentGetPainted(true),
+        mForceMousewheelAutodir(false),
+        mForceMousewheelAutodirHonourRoot(false),
+        mIsPaginatedPresentation(false),
+        mOverscrollBehavior() {}
+
+  bool operator==(const ScrollMetadata& aOther) const {
+    return mMetrics == aOther.mMetrics && mSnapInfo == aOther.mSnapInfo &&
+           mScrollParentId == aOther.mScrollParentId &&
+           // don't compare mContentDescription
+           mLineScrollAmount == aOther.mLineScrollAmount &&
+           mPageScrollAmount == aOther.mPageScrollAmount &&
+           mHasScrollgrab == aOther.mHasScrollgrab &&
+           mIsLayersIdRoot == aOther.mIsLayersIdRoot &&
+           mIsAutoDirRootContentRTL == aOther.mIsAutoDirRootContentRTL &&
+           mForceDisableApz == aOther.mForceDisableApz &&
+           mResolutionUpdated == aOther.mResolutionUpdated &&
+           mIsRDMTouchSimulationActive == aOther.mIsRDMTouchSimulationActive &&
+           mDidContentGetPainted == aOther.mDidContentGetPainted &&
+           mForceMousewheelAutodir == aOther.mForceMousewheelAutodir &&
+           mForceMousewheelAutodirHonourRoot ==
+               aOther.mForceMousewheelAutodirHonourRoot &&
+           mIsPaginatedPresentation == aOther.mIsPaginatedPresentation &&
+           mDisregardedDirection == aOther.mDisregardedDirection &&
+           mOverscrollBehavior == aOther.mOverscrollBehavior &&
+           mScrollUpdates == aOther.mScrollUpdates;
+  }
+
+  bool operator!=(const ScrollMetadata& aOther) const {
+    return !operator==(aOther);
+  }
+
+  bool IsDefault() const {
+    ScrollMetadata def;
+
+    def.mMetrics.SetPresShellId(mMetrics.GetPresShellId());
+    return (def == *this);
+  }
+
+  FrameMetrics& GetMetrics() { return mMetrics; }
+  const FrameMetrics& GetMetrics() const { return mMetrics; }
+
+  void SetSnapInfo(ScrollSnapInfo&& aSnapInfo) {
+    mSnapInfo = std::move(aSnapInfo);
+  }
+  const ScrollSnapInfo& GetSnapInfo() const { return mSnapInfo; }
+
+  ViewID GetScrollParentId() const { return mScrollParentId; }
+
+  void SetScrollParentId(ViewID aParentId) { mScrollParentId = aParentId; }
+  const nsCString& GetContentDescription() const { return mContentDescription; }
+  void SetContentDescription(const nsCString& aContentDescription) {
+    mContentDescription = aContentDescription;
+  }
+  const LayoutDeviceIntSize& GetLineScrollAmount() const {
+    return mLineScrollAmount;
+  }
+  void SetLineScrollAmount(const LayoutDeviceIntSize& size) {
+    mLineScrollAmount = size;
+  }
+  const LayoutDeviceIntSize& GetPageScrollAmount() const {
+    return mPageScrollAmount;
+  }
+  void SetPageScrollAmount(const LayoutDeviceIntSize& size) {
+    mPageScrollAmount = size;
+  }
+  void SetHasScrollgrab(bool aHasScrollgrab) {
+    mHasScrollgrab = aHasScrollgrab;
+  }
+  bool GetHasScrollgrab() const { return mHasScrollgrab; }
+  void SetIsLayersIdRoot(bool aValue) { mIsLayersIdRoot = aValue; }
+  bool IsLayersIdRoot() const { return mIsLayersIdRoot; }
+  void SetIsAutoDirRootContentRTL(bool aValue) {
+    mIsAutoDirRootContentRTL = aValue;
+  }
+  bool IsAutoDirRootContentRTL() const { return mIsAutoDirRootContentRTL; }
+  void SetForceDisableApz(bool aForceDisable) {
+    mForceDisableApz = aForceDisable;
+  }
+  bool IsApzForceDisabled() const { return mForceDisableApz; }
+  void SetResolutionUpdated(bool aUpdated) { mResolutionUpdated = aUpdated; }
+  bool IsResolutionUpdated() const { return mResolutionUpdated; }
+
+  void SetIsRDMTouchSimulationActive(bool aValue) {
+    mIsRDMTouchSimulationActive = aValue;
+  }
+  bool GetIsRDMTouchSimulationActive() const {
+    return mIsRDMTouchSimulationActive;
+  }
+
+  void SetForceMousewheelAutodir(bool aValue) {
+    mForceMousewheelAutodir = aValue;
+  }
+  bool ForceMousewheelAutodir() const { return mForceMousewheelAutodir; }
+
+  void SetForceMousewheelAutodirHonourRoot(bool aValue) {
+    mForceMousewheelAutodirHonourRoot = aValue;
+  }
+  bool ForceMousewheelAutodirHonourRoot() const {
+    return mForceMousewheelAutodirHonourRoot;
+  }
+
+  void SetIsPaginatedPresentation(bool aValue) {
+    mIsPaginatedPresentation = aValue;
+  }
+  bool IsPaginatedPresentation() const { return mIsPaginatedPresentation; }
+
+  bool DidContentGetPainted() const { return mDidContentGetPainted; }
+
+ private:
+  // For use in IPC only
+  void SetDidContentGetPainted(bool aValue) { mDidContentGetPainted = aValue; }
+
+ public:
+  // For more details about the concept of a disregarded direction, refer to the
+  // code which defines mDisregardedDirection.
+  Maybe<ScrollDirection> GetDisregardedDirection() const {
+    return mDisregardedDirection;
+  }
+  void SetDisregardedDirection(const Maybe<ScrollDirection>& aValue) {
+    mDisregardedDirection = aValue;
+  }
+
+  void SetOverscrollBehavior(
+      const OverscrollBehaviorInfo& aOverscrollBehavior) {
+    mOverscrollBehavior = aOverscrollBehavior;
+  }
+  const OverscrollBehaviorInfo& GetOverscrollBehavior() const {
+    return mOverscrollBehavior;
+  }
+
+  void SetScrollUpdates(const nsTArray<ScrollPositionUpdate>& aUpdates) {
+    mScrollUpdates = aUpdates;
+  }
+
+  const nsTArray<ScrollPositionUpdate>& GetScrollUpdates() const {
+    return mScrollUpdates;
+  }
+
+  void UpdatePendingScrollInfo(nsTArray<ScrollPositionUpdate>&& aUpdates) {
+    MOZ_ASSERT(!aUpdates.IsEmpty());
+    mMetrics.UpdatePendingScrollInfo(aUpdates.LastElement());
+
+    mDidContentGetPainted = false;
+    mScrollUpdates.Clear();
+    mScrollUpdates.AppendElements(std::move(aUpdates));
+  }
+
+ private:
+  FrameMetrics mMetrics;
+
+  // Information used to determine where to snap to for a given scroll.
+  ScrollSnapInfo mSnapInfo;
+
+  // The ViewID of the scrollable frame to which overscroll should be handed
+  // off.
+  ViewID mScrollParentId;
+
+  // A description of the content element corresponding to this frame.
+  // This is empty unless this is a scrollable layer and the
+  // apz.printtree pref is turned on.
+  nsCString mContentDescription;
+
+  // The value of GetLineScrollAmount(), for scroll frames.
+  LayoutDeviceIntSize mLineScrollAmount;
+
+  // The value of GetPageScrollAmount(), for scroll frames.
+  LayoutDeviceIntSize mPageScrollAmount;
+
+  // Whether or not this frame is for an element marked 'scrollgrab'.
+  bool mHasScrollgrab : 1;
+
+  // Whether these framemetrics are for the root scroll frame (root element if
+  // we don't have a root scroll frame) for its layers id.
+  bool mIsLayersIdRoot : 1;
+
+  // The AutoDirRootContent is the <body> element in an HTML document, or the
+  // root scrollframe if there is no body. This member variable indicates
+  // whether this element's content in the horizontal direction starts from
+  // right to left (e.g. it's true either if "writing-mode: vertical-rl", or
+  // "writing-mode: horizontal-tb; direction: rtl" in CSS).
+  // When we do auto-dir scrolling (@see mozilla::WheelDeltaAdjustmentStrategy
+  // or refer to bug 1358017 for details), setting a pref can make the code use
+  // the writing mode of this root element instead of the target scrollframe,
+  // and so we need to know if the writing mode is RTL or not.
+  bool mIsAutoDirRootContentRTL : 1;
+
+  // Whether or not the compositor should actually do APZ-scrolling on this
+  // scrollframe.
+  bool mForceDisableApz : 1;
+
+  // Whether the pres shell resolution stored in mMetrics reflects a change
+  // originated by the main thread.
+  bool mResolutionUpdated : 1;
+
+  // Whether or not RDM and touch simulation are active for this document.
+  // It's important to note that if RDM is active then this field will be
+  // true for the content document but NOT the chrome document containing
+  // the browser UI and RDM controls.
+  bool mIsRDMTouchSimulationActive : 1;
+
+  // Whether this metadata is part of a transaction that also repainted the
+  // content (i.e. updated the displaylist or textures). This gets set to false
+  // for "paint-skip" transactions, where the main thread doesn't repaint but
+  // instead requests APZ to update the compositor scroll offset instead. APZ
+  // needs to be able to distinguish these paint-skip transactions so that it
+  // can use the correct transforms.
+  bool mDidContentGetPainted : 1;
+
+  // Whether privileged code has requested that autodir behaviour be
+  // enabled for the scroll frame.
+  bool mForceMousewheelAutodir : 1;
+  bool mForceMousewheelAutodirHonourRoot : 1;
+
+  // Whether this content is being displayed in a paginated fashion
+  // such as printing or print preview. In such cases, content that
+  // would normally only generate one display item may generated one
+  // display item per page, and the different instances may be subject
+  // to different transforms, which constrains the assumptions APZ can make.
+  bool mIsPaginatedPresentation : 1;
+
+  // The disregarded direction means the direction which is disregarded anyway,
+  // even if the scroll frame overflows in that direction and the direction is
+  // specified as scrollable. This could happen in some scenarios, for instance,
+  // a single-line text control frame should disregard wheel scroll in
+  // its block-flow direction even if it overflows in that direction.
+  Maybe<ScrollDirection> mDisregardedDirection;
+
+  // The overscroll behavior for this scroll frame.
+  OverscrollBehaviorInfo mOverscrollBehavior;
+
+  // The ordered list of scroll position updates for this scroll frame since
+  // the last transaction.
+  CopyableTArray<ScrollPositionUpdate> mScrollUpdates;
+
+  // WARNING!!!!
+  //
+  // When adding new fields to ScrollMetadata, the following places should be
+  // updated to include them (as needed):
+  //    1. ScrollMetadata::operator ==
+  //    2. AsyncPanZoomController::NotifyLayersUpdated
+  //    3. The ParamTraits specialization in LayersMessageUtils.h
+  //
+  // Please add new fields above this comment.
+};
+
+typedef nsTHashMap<ScrollableLayerGuid::ViewIDHashKey,
+                   nsTArray<ScrollPositionUpdate>>
+    ScrollUpdatesMap;
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif /* GFX_FRAMEMETRICS_H */
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