[Cleanup] Factor out layout store code from DisplayController

ash/display/display_manager.h

Index: ash/display/display_manager.h
diff --git a/ash/display/display_manager.h b/ash/display/display_manager.h
index 3d7561657ba9d1d742e9b77ab080d3bafb4a8dd7..8a1b3f78ee2db1384718aae6e45dec56d6e38b11 100644
--- a/ash/display/display_manager.h
+++ b/ash/display/display_manager.h
@@ -34,6 +34,7 @@ class DisplayManagerTestApi;
 class SystemGestureEventFilterTest;
 }
 namespace internal {
+class DisplayLayoutStore;
 
 // DisplayManager maintains the current display configurations,
 // and notifies observers when configuration changes.
@@ -61,6 +62,10 @@ class ASH_EXPORT DisplayManager :
       const gfx::Display& primary_display,
       gfx::Display* secondary_display);
 
+  DisplayLayoutStore* layout_store() {
+    return layout_store_.get();
+  }
+
   // When set to true, the MonitorManager calls OnDisplayBoundsChanged
   // even if the display's bounds didn't change. Used to swap primary
   // display.
@@ -238,6 +243,8 @@ private:
   bool UpdateSecondaryDisplayBoundsForLayout(DisplayList* display_list,
                                              size_t* updated_index) const;
 
+  scoped_ptr<DisplayLayoutStore> layout_store_;
+
   int64 first_display_id_;
 
   gfx::Display mirrored_display_;