ash: Start/stop observing KeyboardController via ShellObserver

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 7661de4e0aa7ee3d54195f17152552f62666fece..168624371e1499f73fbe8acd150424f4f0d05922 100644
--- a/ash/common/shelf/shelf_layout_manager.h
+++ b/ash/common/shelf/shelf_layout_manager.h
@@ -18,12 +18,17 @@
 #include "ash/public/cpp/shelf_types.h"
 #include "base/macros.h"
 #include "base/observer_list.h"
+#include "base/scoped_observer.h"
 #include "base/timer/timer.h"
 #include "ui/gfx/geometry/insets.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/keyboard/keyboard_controller_observer.h"
 #include "ui/wm/public/activation_change_observer.h"
 
+namespace keyboard {
+class KeyboardController;
+}
+
 namespace ui {
 class ImplicitAnimationObserver;
 class MouseEvent;
@@ -180,6 +185,10 @@ class ASH_EXPORT ShelfLayoutManager
   // available work area from the top of the screen.
   void SetChromeVoxPanelHeight(int height);
 
+  void StartObservingKeyboard(
+      keyboard::KeyboardController* keyboard_controller);
+  void StopObservingKeyboard(keyboard::KeyboardController* keyboard_controller);
+
  private:
   class UpdateShelfObserver;
   friend class PanelLayoutManagerTest;
@@ -358,6 +367,10 @@ class ASH_EXPORT ShelfLayoutManager
   // MaybeUpdateShelfBackground() instead.
   ShelfBackgroundType shelf_background_type_;
 
+  ScopedObserver<keyboard::KeyboardController,
+                 keyboard::KeyboardControllerObserver>
+      keyboard_observer_;
+
   DISALLOW_COPY_AND_ASSIGN(ShelfLayoutManager);
 };