Preserve fractional scroll offset for JS scrolling API

Source/platform/scroll/ScrollView.h

 /*
  * Copyright (C) 2004, 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Holger Hans Peter Freyther
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 116 matching lines @@
     // values).
     virtual IntSize contentsSize() const override; // Always at least as big as the visibleWidth()/visibleHeight().
     int contentsWidth() const { return contentsSize().width(); }
     int contentsHeight() const { return contentsSize().height(); }
     virtual void setContentsSize(const IntSize&);
 
     // Functions for querying the current scrolled position (both as a point, a size, or as individual X and Y values).
     // FIXME: Remove the IntPoint version. crbug.com/414283.
     virtual IntPoint scrollPosition() const override { return visibleContentRect().location(); }
     virtual DoublePoint scrollPositionDouble() const override { return m_scrollPosition; }
+    // FIXME: Remove scrollOffset(). crbug.com/414283.
     IntSize scrollOffset() const { return toIntSize(visibleContentRect().location()); } // Gets the scrolled position as an IntSize. Convenient for adding to other sizes.
+    DoubleSize scrollOffsetDouble() const { return DoubleSize(m_scrollPosition.x(), m_scrollPosition.y()); }
     DoubleSize pendingScrollDelta() const { return m_pendingScrollDelta; }
     virtual IntPoint maximumScrollPosition() const override; // The maximum position we can be scrolled to.
     virtual IntPoint minimumScrollPosition() const override; // The minimum position we can be scrolled to.
     // Adjust the passed in scroll position to keep it between the minimum and maximum positions.
     IntPoint adjustScrollPositionWithinRange(const IntPoint&) const;
     DoublePoint adjustScrollPositionWithinRange(const DoublePoint&) const;
     double scrollX() const { return scrollPositionDouble().x(); }
     double scrollY() const { return scrollPositionDouble().y(); }
 
     virtual IntSize overhangAmount() const override;
 
     void cacheCurrentScrollPosition() { m_cachedScrollPosition = scrollPositionDouble(); }
     DoublePoint cachedScrollPosition() const { return m_cachedScrollPosition; }
 
     // Functions for scrolling the view.
-    virtual void setScrollPosition(const IntPoint&, ScrollBehavior = ScrollBehaviorInstant);
-    void scrollBy(const IntSize& s, ScrollBehavior behavior = ScrollBehaviorInstant)
+    virtual void setScrollPosition(const DoublePoint&, ScrollBehavior = ScrollBehaviorInstant);
+    void scrollBy(const DoubleSize& s, ScrollBehavior behavior = ScrollBehaviorInstant)
     {
-        return setScrollPosition(scrollPosition() + s, behavior);
+        return setScrollPosition(scrollPositionDouble() + s, behavior);
     }
 
     bool scroll(ScrollDirection, ScrollGranularity);
 
     // Scroll the actual contents of the view (either blitting or invalidating as needed).
     void scrollContents(const IntSize& scrollDelta);
 
     // This gives us a means of blocking painting on our scrollbars until the first layout has occurred.
     void setScrollbarsSuppressed(bool suppressed, bool repaintOnUnsuppress = false);
     bool scrollbarsSuppressed() const { return m_scrollbarsSuppressed; }
@@ skipping 116 matching lines @@
 
     enum ComputeScrollbarExistenceOption {
         FirstPass,
         Incremental
     };
     void computeScrollbarExistence(bool& newHasHorizontalScrollbar, bool& newHasVerticalScrollbar, const IntSize& docSize, ComputeScrollbarExistenceOption = FirstPass) const;
     void updateScrollbarGeometry();
     IntRect adjustScrollbarRectForResizer(const IntRect&, Scrollbar*);
 
     // Called to update the scrollbars to accurately reflect the state of the view.
-    void updateScrollbars(const IntSize& desiredOffset);
+    void updateScrollbars(const DoubleSize& desiredOffset);
 
     IntSize excludeScrollbars(const IntSize&) const;
 
     class InUpdateScrollbarsScope {
     public:
         explicit InUpdateScrollbarsScope(ScrollView* view)
             : m_scope(view->m_inUpdateScrollbars, true)
         { }
     private:
         TemporaryChange<bool> m_scope;
     };
 
     virtual bool scrollbarsDisabled() const { return false; }
 
 private:
     bool adjustScrollbarExistence(ComputeScrollbarExistenceOption = FirstPass);
     void adjustScrollbarOpacity();
     // FIXME(bokan): setScrollOffset, setScrollPosition, scrollTo, scrollToOffsetWithoutAnimation,
     // notifyScrollPositionChanged...there's too many ways to scroll this class. This needs
     // some cleanup.
-    void setScrollOffsetFromUpdateScrollbars(const IntSize&);
+    void setScrollOffsetFromUpdateScrollbars(const DoubleSize&);
 
     RefPtr<Scrollbar> m_horizontalScrollbar;
     RefPtr<Scrollbar> m_verticalScrollbar;
     ScrollbarMode m_horizontalScrollbarMode;
     ScrollbarMode m_verticalScrollbarMode;
 
     bool m_horizontalScrollbarLock;
     bool m_verticalScrollbarLock;
 
     HashSet<RefPtr<Widget> > m_children;
@@ skipping 20 matching lines @@
 
     void calculateOverhangAreasForPainting(IntRect& horizontalOverhangRect, IntRect& verticalOverhangRect);
     void updateOverhangAreas();
 }; // class ScrollView
 
 DEFINE_TYPE_CASTS(ScrollView, Widget, widget, widget->isScrollView(), widget.isScrollView());
 
 } // namespace blink
 
 #endif // ScrollView_h