Change Page::m_mainFrame to be a Frame.

Source/core/page/CreateWindow.cpp

Index: Source/core/page/CreateWindow.cpp
diff --git a/Source/core/page/CreateWindow.cpp b/Source/core/page/CreateWindow.cpp
index ab39dfa0a92d54b29fb2ce48ea61c0a75038cf15..7289d186c36f91956af366e79087dc7b9b138d54 100644
--- a/Source/core/page/CreateWindow.cpp
+++ b/Source/core/page/CreateWindow.cpp
@@ -76,12 +76,12 @@ static LocalFrame* createWindow(LocalFrame& openerFrame, LocalFrame& lookupFrame
         return 0;
 
     Page* page = oldPage->chrome().client().createWindow(&openerFrame, request, features, policy, shouldSendReferrer);
-    if (!page)
+    if (!page || !page->mainFrame()->isLocalFrame())
         return 0;
     FrameHost* host = &page->frameHost();
 
     ASSERT(page->mainFrame());
-    LocalFrame& frame = *page->mainFrame();
+    LocalFrame& frame = *page->deprecatedLocalMainFrame();
 
     if (request.frameName() != "_blank")
         frame.tree().setName(request.frameName());