Add Frame::isMainFrame and deploy it

Source/core/page/AutoscrollController.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2012 Digia Plc. and/or its subsidiary(-ies)
  *
  * 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
@@ skipping 153 matching lines @@
         startAutoscroll();
     } else if (m_autoscrollRenderer != scrollable) {
         m_dragAndDropAutoscrollStartTime = eventTime;
         m_autoscrollRenderer = scrollable;
     }
 }
 
 #if OS(WIN)
 void AutoscrollController::handleMouseReleaseForPanScrolling(Frame* frame, const PlatformMouseEvent& mouseEvent)
 {
-    Page* page = frame->page();
-    if (!page || page->mainFrame() != frame)
+    if (!frame->isMainFrame())
         return;
     switch (m_autoscrollType) {
     case AutoscrollForPan:
         if (mouseEvent.button() == MiddleButton)
             m_autoscrollType = AutoscrollForPanCanStop;
         break;
     case AutoscrollForPanCanStop:
         stopAutoscroll();
         break;
     }
@@ skipping 102 matching lines @@
     } else if (east)
         view->setCursor(eastPanningCursor());
     else if (west)
         view->setCursor(westPanningCursor());
     else
         view->setCursor(middlePanningCursor());
 }
 #endif
 
 } // namespace WebCore