Change Page::m_mainFrame to be a Frame.

Source/core/loader/FrameLoader.cpp

Index: Source/core/loader/FrameLoader.cpp
diff --git a/Source/core/loader/FrameLoader.cpp b/Source/core/loader/FrameLoader.cpp
index 769c8a81a9010a994cbfa562583eb0dc23ed9d49..29c05351ac0eb9944075503e2c79c3593c893346 100644
--- a/Source/core/loader/FrameLoader.cpp
+++ b/Source/core/loader/FrameLoader.cpp
@@ -1077,8 +1077,10 @@ void FrameLoader::detachChildren()
 void FrameLoader::checkLoadComplete()
 {
     ASSERT(client()->hasWebView());
-    if (Page* page = m_frame->page())
-        page->mainFrame()->loader().checkLoadCompleteForThisFrame();
+    if (Page* page = m_frame->page()) {
+        if (page->mainFrame()->isLocalFrame())
+            toLocalFrame(page->mainFrame())->loader().checkLoadCompleteForThisFrame();
+    }
 }
 
 String FrameLoader::userAgent(const KURL& url) const