Split the frame tree logic out of HistoryItem

Source/core/page/Page.h

Index: Source/core/page/Page.h
diff --git a/Source/core/page/Page.h b/Source/core/page/Page.h
index ce0b451966a4a7695f28db85d2aca1618794e2a9..e988d1af69bd7579158d67aba2a4de345c31d6ef 100644
--- a/Source/core/page/Page.h
+++ b/Source/core/page/Page.h
@@ -52,6 +52,7 @@ class FocusController;
 class Frame;
 class FrameSelection;
 class HaltablePlugin;
+class HistoryController;
 class HistoryItem;
 class InspectorClient;
 class InspectorController;
@@ -112,6 +113,8 @@ public:
 
     EditorClient& editorClient() const { return *m_editorClient; }
 
+    HistoryController* history() const { return m_history.get(); }
+
     void setMainFrame(PassRefPtr<Frame>);
     Frame* mainFrame() const { return m_mainFrame.get(); }
 
@@ -264,6 +267,7 @@ private:
     const OwnPtr<PointerLockController> m_pointerLockController;
     RefPtr<ScrollingCoordinator> m_scrollingCoordinator;
 
+    const OwnPtr<HistoryController> m_history;
     const OwnPtr<Settings> m_settings;
     const OwnPtr<ProgressTracker> m_progress;