ash: Start/stop observing KeyboardController via ShellObserver

ash/common/wm/panels/panel_layout_manager.h

Index: ash/common/wm/panels/panel_layout_manager.h
diff --git a/ash/common/wm/panels/panel_layout_manager.h b/ash/common/wm/panels/panel_layout_manager.h
index 65c19abdd3b3e58656fe0c5f1645cc00e8f750d1..4d41369b785ee546144b8cb89455be4e51438ecf 100644
--- a/ash/common/wm/panels/panel_layout_manager.h
+++ b/ash/common/wm/panels/panel_layout_manager.h
@@ -18,6 +18,7 @@
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
+#include "base/scoped_observer.h"
 #include "ui/aura/window_observer.h"
 #include "ui/aura/window_tracker.h"
 #include "ui/keyboard/keyboard_controller.h"
@@ -117,6 +118,10 @@ class ASH_EXPORT PanelLayoutManager
   void WillChangeVisibilityState(ShelfVisibilityState new_state) override;
   void OnShelfIconPositionsChanged() override;
 
+  void StartObservingKeyboard(
+      keyboard::KeyboardController* keyboard_controller);
+  void StopObservingKeyboard(keyboard::KeyboardController* keyboard_controller);
+
  private:
   friend class PanelLayoutManagerTest;
   friend class PanelWindowResizerTest;
@@ -196,6 +201,11 @@ class ASH_EXPORT PanelLayoutManager
   // The last active panel. Used to maintain stacking order even if no panels
   // are currently focused.
   WmWindow* last_active_panel_;
+
+  ScopedObserver<keyboard::KeyboardController,
+                 keyboard::KeyboardControllerObserver>
+      keyboard_observer_;
+
   base::WeakPtrFactory<PanelLayoutManager> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(PanelLayoutManager);