Round visual rects when crossing frame boundaries.

third_party/WebKit/Source/core/layout/LayoutView.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 511 matching lines @@
             if (visibleRectFlags & EdgeInclusive) {
                 if (!rect.inclusiveIntersect(viewRectangle))
                     return false;
             } else {
                 rect.intersect(viewRectangle);
             }
 
             // Adjust for scroll offset of the view.
             rect.moveBy(-viewRectangle.location());
         }
+        // Frames are painted at rounded-int position. Since we cannot efficiently compute the subpixel offset
+        // of painting at this point in a a bottom-up walk, round to the enclosing int rect, which will enclose
+        // the actual visible rect.
+        rect = LayoutRect(enclosingIntRect(rect));
 
         // Adjust for frame border.
         rect.move(obj->contentBoxOffset());
         return obj->mapToVisibleRectInAncestorSpace(ancestor, rect, visibleRectFlags);
     }
 
     return true;
 }
 
 void LayoutView::adjustOffsetForFixedPosition(LayoutRect& rect) const
@@ skipping 496 matching lines @@
 
 ScrollResult LayoutView::scroll(ScrollGranularity granularity, const FloatSize& delta)
 {
     if (!frameView())
         return ScrollResult();
 
     return frame()->applyScrollDelta(granularity, delta, false);
 }
 
 } // namespace blink