Update PaintLayer size during layout, not after.

third_party/WebKit/Source/core/frame/FrameView.h

 /*
    Copyright (C) 1997 Martin Jones (mjones@kde.org)
              (C) 1998 Waldo Bastian (bastian@kde.org)
              (C) 1998, 1999 Torben Weis (weis@kde.org)
              (C) 1999 Lars Knoll (knoll@kde.org)
              (C) 1999 Antti Koivisto (koivisto@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
@@ skipping 210 matching lines @@
   float InputEventsScaleFactor() const;
 
   // Offset used to convert incoming input events while emulating device metics.
   IntSize InputEventsOffsetForEmulation() const;
   void SetInputEventsTransformForEmulation(const IntSize&, float);
 
   void DidChangeScrollOffset();
   void DidUpdateElasticOverscroll();
 
   void ViewportSizeChanged(bool width_changed, bool height_changed);
+  void MarkViewportConstrainedObjectsForLayout(bool width_changed,
+                                               bool height_changed);
 
   AtomicString MediaType() const;
   void SetMediaType(const AtomicString&);
   void AdjustMediaTypeForPrinting(bool printing);
 
   WebDisplayMode DisplayMode() { return display_mode_; }
   void SetDisplayMode(WebDisplayMode);
 
   DisplayShape GetDisplayShape() { return display_shape_; }
   void SetDisplayShape(DisplayShape);
@@ skipping 1032 matching lines @@
                   frameViewBase.IsFrameView());
 DEFINE_TYPE_CASTS(FrameView,
                   ScrollableArea,
                   scrollableArea,
                   scrollableArea->IsFrameView(),
                   scrollableArea.IsFrameView());
 
 }  // namespace blink
 
 #endif  // FrameView_h