Change Page::m_mainFrame to be a Frame.

Source/core/inspector/InspectorDOMAgent.cpp

Index: Source/core/inspector/InspectorDOMAgent.cpp
diff --git a/Source/core/inspector/InspectorDOMAgent.cpp b/Source/core/inspector/InspectorDOMAgent.cpp
index 10d432c7c3f350d9ff0e6cc8c16cf66657fc3a7b..d94bd36b934fef751112d6be502f56ae7686ff12 100644
--- a/Source/core/inspector/InspectorDOMAgent.cpp
+++ b/Source/core/inspector/InspectorDOMAgent.cpp
@@ -1777,13 +1777,13 @@ void InspectorDOMAgent::didCommitLoad(LocalFrame* frame, DocumentLoader* loader)
     // FIXME: If "frame" is always guarenteed to be in the same Page as loader->frame()
     // then all we need to check here is loader->frame()->isMainFrame()
     // and we don't need "frame" at all.
-    LocalFrame* mainFrame = frame->page()->mainFrame();
+    Frame* mainFrame = frame->page()->mainFrame();
     if (loader->frame() != mainFrame) {
         invalidateFrameOwnerElement(loader->frame());
         return;
     }
 
-    setDocument(mainFrame->document());
+    setDocument(mainFrame->isLocalFrame() ? toLocalFrame(mainFrame)->document() : 0);
 }
 
 void InspectorDOMAgent::didInsertDOMNode(Node* node)