Change Page::m_mainFrame to be a Frame.

Source/core/inspector/InspectorLayerTreeAgent.cpp

Index: Source/core/inspector/InspectorLayerTreeAgent.cpp
diff --git a/Source/core/inspector/InspectorLayerTreeAgent.cpp b/Source/core/inspector/InspectorLayerTreeAgent.cpp
index c67d199034d02452865a1d1091fc7fabd73df71c..5b2a5897a5319633735187a327c69908b155b007 100644
--- a/Source/core/inspector/InspectorLayerTreeAgent.cpp
+++ b/Source/core/inspector/InspectorLayerTreeAgent.cpp
@@ -169,7 +169,7 @@ void InspectorLayerTreeAgent::restore()
 void InspectorLayerTreeAgent::enable(ErrorString*)
 {
     m_instrumentingAgents->setInspectorLayerTreeAgent(this);
-    if (LocalFrame* frame = m_page->mainFrame()) {
+    if (LocalFrame* frame = toLocalFrame(m_page->mainFrame())) {
         Document* document = frame->document();
         if (document && document->lifecycle().state() >= DocumentLifecycle::CompositingClean)
             layerTreeDidChange();
@@ -253,7 +253,7 @@ int InspectorLayerTreeAgent::idForNode(Node* node)
 
 RenderLayerCompositor* InspectorLayerTreeAgent::renderLayerCompositor()
 {
-    RenderView* renderView = m_page->mainFrame()->contentRenderer();
+    RenderView* renderView = toLocalFrame(m_page->mainFrame())->contentRenderer();
     RenderLayerCompositor* compositor = renderView ? renderView->compositor() : 0;
     return compositor;
 }