FrameView's size should be calculated based on contentWidth+scrollbarWidth

Source/web/PageScaleConstraintsSet.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 57 matching lines @@
     // This should be set to true on each page load to note that the page scale
     // factor needs to be reset to its initial value.
     void setNeedsReset(bool);
     bool needsReset() const { return m_needsReset; }
 
     // This is set when one of the inputs to finalConstraints changes.
     bool constraintsDirty() const { return m_constraintsDirty; }
 
     void didChangeViewSize(const IntSize&);
 
-    IntSize mainFrameSize(const IntSize& contentsSize) const;
+    IntSize mainFrameSize(int contentWidthIncludingScrollbar) const;
 
 private:
     PageScaleConstraints computeConstraintsStack() const;
 
     PageScaleConstraints m_pageDefinedConstraints;
     PageScaleConstraints m_userAgentConstraints;
     PageScaleConstraints m_finalConstraints;
 
     int m_lastContentsWidth;
     IntSize m_viewSize;
 
     bool m_needsReset;
     bool m_constraintsDirty;
 };
 
 } // namespace blink
 
 #endif // PageScaleConstraintsSet_h