Add Frame::isMainFrame and deploy it

Source/core/rendering/RenderGeometryMap.cpp

 /*
  * Copyright (C) 2012 Apple 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:
  * 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 313 matching lines @@
 bool RenderGeometryMap::isTopmostRenderView(const RenderObject* renderer) const
 {
     if (!renderer->isRenderView())
         return false;
 
     // If we're not working with multiple RenderViews, then any view is considered
     // "topmost" (to preserve original behavior).
     if (!(m_mapCoordinatesFlags & TraverseDocumentBoundaries))
         return true;
 
-    Frame* thisFrame = renderer->frame();
-    return thisFrame == thisFrame->page()->mainFrame();
+    return renderer->frame()->isMainFrame();
 }
 #endif
 
 } // namespace WebCore