Delay scrollContents until the next paint

Source/core/rendering/RenderView.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 478 matching lines @@
 
     if (style()->isFlippedBlocksWritingMode()) {
         // We have to flip by hand since the view's logical height has not been determined.  We
         // can use the viewport width and height.
         if (style()->isHorizontalWritingMode())
             rect.setY(viewHeight() - rect.maxY());
         else
             rect.setX(viewWidth() - rect.maxX());
     }
 
-    if (fixed && m_frameView)
+    if (fixed && m_frameView) {
         rect.move(m_frameView->scrollOffsetForFixedPosition());
+        // If we're in the middle of scrolling, also invalidate the previous scroll position.

[abarth-chromium, 2014/03/08 06:54:52]

I might say that we have a pending scroll delta rather than saying we're in the
middle of a scroll.

[ykyyip, 2014/03/11 01:59:39]

Done.

+        if (!m_frameView->scrollDelta().isZero()) {
+            LayoutRect scrolledPrev = rect;
+            scrolledPrev.move(-m_frameView->scrollDelta());
+            rect.unite(scrolledPrev);
+        }
+    }
 
     // Apply our transform if we have one (because of full page zooming).
     if (!repaintContainer && layer() && layer()->transform())
         rect = layer()->transform()->mapRect(rect);
 }
 
 void RenderView::absoluteRects(Vector<IntRect>& rects, const LayoutPoint& accumulatedOffset) const
 {
     rects.append(pixelSnappedIntRect(accumulatedOffset, layer()->size()));
 }
@@ skipping 480 matching lines @@
     return viewWidth(IncludeScrollbars) / scale;
 }
 
 double RenderView::layoutViewportHeight() const
 {
     float scale = m_frameView ? m_frameView->frame().pageZoomFactor() : 1;
     return viewHeight(IncludeScrollbars) / scale;
 }
 
 } // namespace WebCore