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 bcfe290cf9a39a416c622eba2b51b799a5707e92..cae9ff8a848050c9528a65fbf6705e12bf5e50d5 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;
@@ -111,6 +112,8 @@ 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(); }
 
@@ -262,6 +265,7 @@ 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;