mash: Remove WmRootWindowControllerObserver.

ash/common/shelf/shelf_layout_manager.h

Index: ash/common/shelf/shelf_layout_manager.h
diff --git a/ash/common/shelf/shelf_layout_manager.h b/ash/common/shelf/shelf_layout_manager.h
index aae684e4ae8afb06a40d8ce462abf91b66fdc847..b16b13df676cf483b3b61d2a4affcd4285f3ea9e 100644
--- a/ash/common/shelf/shelf_layout_manager.h
+++ b/ash/common/shelf/shelf_layout_manager.h
@@ -186,7 +186,6 @@ class ASH_EXPORT ShelfLayoutManager
   void SetChromeVoxPanelHeight(int height);
 
  private:
-  class RootWindowControllerObserverImpl;
   class UpdateShelfObserver;
   friend class PanelLayoutManagerTest;
   friend class ShelfLayoutManagerTest;
@@ -372,9 +371,6 @@ class ASH_EXPORT ShelfLayoutManager
   // TODO(oshima): Remove this when MD immersive is launched.
   bool invisible_auto_hide_shelf_ = false;
 
-  std::unique_ptr<RootWindowControllerObserverImpl>
-      root_window_controller_observer_;
-
   DISALLOW_COPY_AND_ASSIGN(ShelfLayoutManager);
 };