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 1912e6c3797b1e71edd403aa3f9521b19ab39d59..3dbebffcc004b8b14126ffbf7d94bd82c6775ae7 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
@@ -216,17 +216,17 @@ 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
+  // 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 DelayScrollPositionClampScope {
+  class DelayScrollOffsetClampScope {
     STACK_ALLOCATED();
 
    public:
-    DelayScrollPositionClampScope();
-    ~DelayScrollPositionClampScope();
+    DelayScrollOffsetClampScope();
+    ~DelayScrollOffsetClampScope();
 
     static bool clampingIsDelayed() { return s_count; }
     static void setNeedsClamp(PaintLayerScrollableArea*);
@@ -290,10 +290,10 @@ 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;
@@ -313,24 +313,20 @@ class CORE_EXPORT PaintLayerScrollableArea final
   ScrollBehavior scrollBehaviorStyle() const override;
   CompositorAnimationTimeline* compositorAnimationTimeline() const override;
 
-  DoubleSize scrollOffset() const { return m_scrollOffset; }
-
   // FIXME: We shouldn't allow access to m_overflowRect outside this class.
   LayoutRect overflowRect() const { return m_overflowRect; }
 
-  void scrollToOffset(const DoubleSize& scrollOffset,
-                      ScrollBehavior scrollBehavior = ScrollBehaviorInstant,
-                      ScrollType scrollType = ProgrammaticScroll) {
-    ScrollableArea::setScrollPosition(-scrollOrigin() + scrollOffset,
-                                      scrollType, scrollBehavior);
+  void scrollToAbsolutePosition(
+      const FloatPoint& position,
+      ScrollBehavior scrollBehavior = ScrollBehaviorInstant,
+      ScrollType scrollType = ProgrammaticScroll) {
+    setScrollOffset(position - scrollOrigin(), scrollType, scrollBehavior);
   }
 
-  void setScrollPosition(
-      const DoublePoint& position,
-      ScrollType scrollType,
-      ScrollBehavior scrollBehavior = ScrollBehaviorInstant) override {
-    scrollToOffset(toDoubleSize(position), scrollBehavior, scrollType);
-  }
+  // 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 setScrollOffsetUnconditionally(const ScrollOffset&,
+                                      ScrollType = ProgrammaticScroll);
 
   // This will set the scroll position without clamping, and it will do all
   // post-update work even if the scroll position didn't change.
@@ -341,7 +337,7 @@ class CORE_EXPORT PaintLayerScrollableArea final
   // 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();
@@ -392,7 +388,7 @@ 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,
@@ -455,13 +451,10 @@ class CORE_EXPORT PaintLayerScrollableArea final
   }
   void resetRebuildScrollbarLayerFlags();
 
-  // Did DelayScrollPositionClampScope prevent us from running
-  // clampScrollPositionsAfterLayout()
-  // in updateAfterLayout()?
-  bool needsScrollPositionClamp() const { return m_needsScrollPositionClamp; }
-  void setNeedsScrollPositionClamp(bool val) {
-    m_needsScrollPositionClamp = val;
-  }
+  // Did DelayScrollOffsetClampScope prevent us from running
+  // clampScrollOffsetsAfterLayout() in updateAfterLayout()?
+  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()?
@@ -511,7 +504,7 @@ class CORE_EXPORT PaintLayerScrollableArea final
   void updateScrollOrigin();
   void updateScrollDimensions();
 
-  void setScrollOffset(const DoublePoint&, ScrollType) override;
+  void updateScrollOffset(const ScrollOffset&, ScrollType) override;
 
   int verticalScrollbarStart(int minX, int maxX) const;
   int horizontalScrollbarStart(int minX) const;
@@ -560,7 +553,7 @@ 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;
@@ -574,8 +567,8 @@ class CORE_EXPORT PaintLayerScrollableArea final
   // ScrollbarManager holds the Scrollbar instances.
   ScrollbarManager m_scrollbarManager;
 
-  // This is the (scroll) offset from scrollOrigin().
-  DoubleSize m_scrollOffset;
+  // This is the offset from the beginning of content flow.
+  ScrollOffset m_scrollOffset;
 
   IntPoint m_cachedOverlayScrollbarOffset;