Use float for scroll offset.

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h

Index: third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
index bf2766edf1621bba431d124f46d26e1ef88a3701..672fbe857abddf6381fcfd72028808ffd2a7c010 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
@@ -214,16 +214,16 @@ class CORE_EXPORT PaintLayerScrollableArea final
     static int s_count;
   };
 
-  // If a DelayScrollPositionClampScope object is alive, updateAfterLayout() will not
-  // clamp scroll positions to ensure they are in the valid range.  When
-  // the last DelayScrollPositionClampScope object is destructed, all PaintLayerScrollableArea's
-  // that delayed clamping their positions will immediately clamp them.
-  class DelayScrollPositionClampScope {
+  // If a DelayScrollOffsetClampScope object is alive, updateAfterLayout() will not
+  // clamp scroll offsets to ensure they are in the valid range.  When
+  // the last DelayScrollOffsetClampScope object is destructed, all PaintLayerScrollableArea's
+  // that delayed clamping their offsets will immediately clamp them.
+  class DelayScrollOffsetClampScope {
     STACK_ALLOCATED();
 
    public:
-    DelayScrollPositionClampScope();
-    ~DelayScrollPositionClampScope();
+    DelayScrollOffsetClampScope();
+    ~DelayScrollOffsetClampScope();
 
     static bool clampingIsDelayed() { return s_count; }
     static void setNeedsClamp(PaintLayerScrollableArea*);
@@ -287,10 +287,10 @@ class CORE_EXPORT PaintLayerScrollableArea final
       const Scrollbar&,
       const IntPoint&) const override;
   int scrollSize(ScrollbarOrientation) const override;
-  IntPoint scrollPosition() const override;
-  DoublePoint scrollPositionDouble() const override;
-  IntPoint minimumScrollPosition() const override;
-  IntPoint maximumScrollPosition() const override;
+  IntSize scrollOffsetInt() const override;
+  ScrollOffset scrollOffset() const override;
+  IntSize minimumScrollOffsetInt() const override;
+  IntSize maximumScrollOffsetInt() const override;
   IntRect visibleContentRect(
       IncludeScrollbarsInRect = ExcludeScrollbars) const override;
   int visibleHeight() const override;
@@ -313,27 +313,26 @@ class CORE_EXPORT PaintLayerScrollableArea final
   // FIXME: We shouldn't allow access to m_overflowRect outside this class.
   LayoutRect overflowRect() const { return m_overflowRect; }
 
-  DoubleSize offsetFromOrigin() const {
-    return toDoubleSize(DoublePoint(scrollOrigin())) + m_scrollPosition;
+  FloatPoint absolutePosition() const {

[bokan, 2016/10/02 19:47:51]

Since scrollOrigin is a ScrollableArea concept, I think this method should be
declared there as well.

[szager1, 2016/10/05 07:43:36]

Done.

+    return FloatPoint(scrollOrigin()) + m_scrollOffset;
   }
-  void scrollToOffsetFromOrigin(
-      const DoubleSize& scrollOffset,
+  void scrollToAbsolutePosition(
+      const FloatPoint& position,
       ScrollBehavior scrollBehavior = ScrollBehaviorInstant,
       ScrollType scrollType = ProgrammaticScroll) {
-    setScrollPosition(-scrollOrigin() + scrollOffset, scrollType,
-                      scrollBehavior);
+    setScrollOffset(position - scrollOrigin(), scrollType, scrollBehavior);
   }
 
-  // This will set the scroll position without clamping, and it will do all post-update
-  // work even if the scroll position didn't change.
-  void setScrollPositionUnconditionally(const DoublePoint&,
-                                        ScrollType = ProgrammaticScroll);
+  // This will set the scroll offset without clamping, and it will do all post-update
+  // work even if the scroll offset didn't change.
+  void setScrollOffsetUnconditionally(const ScrollOffset&,
+                                      ScrollType = ProgrammaticScroll);
 
   // TODO(szager): Actually run these after all of layout is finished.  Currently, they
   // run at the end of box()'es layout (or after all flexbox layout has finished) but while
   // document layout is still happening.
   void updateAfterLayout();
-  void clampScrollPositionsAfterLayout();
+  void clampScrollOffsetsAfterLayout();
 
   void updateAfterStyleChange(const ComputedStyle*);
   void updateAfterOverflowRecalc();
@@ -380,7 +379,7 @@ class CORE_EXPORT PaintLayerScrollableArea final
   bool hitTestResizerInFragments(const PaintLayerFragments&,
                                  const HitTestLocation&) const;
 
-  // Returns the new position, after scrolling, of the given rect in absolute
+  // Returns the new offset, after scrolling, of the given rect in absolute
   // coordinates, clipped by the parent's client rect.
   LayoutRect scrollIntoView(const LayoutRect&,
                             const ScrollAlignment& alignX,
@@ -441,12 +440,10 @@ class CORE_EXPORT PaintLayerScrollableArea final
   }
   void resetRebuildScrollbarLayerFlags();
 
-  // Did DelayScrollPositionClampScope prevent us from running clampScrollPositionsAfterLayout()
+  // Did DelayScrollOffsetClampScope prevent us from running clampScrollOffsetsAfterLayout()
   // in updateAfterLayout()?
-  bool needsScrollPositionClamp() const { return m_needsScrollPositionClamp; }
-  void setNeedsScrollPositionClamp(bool val) {
-    m_needsScrollPositionClamp = val;
-  }
+  bool needsScrollOffsetClamp() const { return m_needsScrollOffsetClamp; }
+  void setNeedsScrollOffsetClamp(bool val) { m_needsScrollOffsetClamp = val; }
 
   // Did PreventRelayoutScope prevent us from running re-layout due to adding/subtracting
   // scrollbars in updateAfterLayout()?
@@ -496,7 +493,7 @@ class CORE_EXPORT PaintLayerScrollableArea final
   void updateScrollOrigin();
   void updateScrollDimensions();
 
-  void updateScrollPosition(const DoublePoint&, ScrollType) override;
+  void updateScrollOffset(const ScrollOffset&, ScrollType) override;
 
   int verticalScrollbarStart(int minX, int maxX) const;
   int horizontalScrollbarStart(int minX) const;
@@ -544,7 +541,7 @@ class CORE_EXPORT PaintLayerScrollableArea final
   unsigned m_rebuildHorizontalScrollbarLayer : 1;
   unsigned m_rebuildVerticalScrollbarLayer : 1;
 
-  unsigned m_needsScrollPositionClamp : 1;
+  unsigned m_needsScrollOffsetClamp : 1;
   unsigned m_needsRelayout : 1;
   unsigned m_hadHorizontalScrollbarBeforeRelayout : 1;
   unsigned m_hadVerticalScrollbarBeforeRelayout : 1;
@@ -558,8 +555,8 @@ class CORE_EXPORT PaintLayerScrollableArea final
   // ScrollbarManager holds the Scrollbar instances.
   ScrollbarManager m_scrollbarManager;
 
-  // This is the absolute scroll position, *not* relative to m_scrollOrigin.
-  DoubleSize m_scrollPosition;
+  // This is the offset from the beginning of content flow.
+  ScrollOffset m_scrollOffset;
 
   IntPoint m_cachedOverlayScrollbarOffset;