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..652549557befd6f8bd399daf1fc875489f0c9ecf 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;
@@ -135,6 +140,8 @@ class ASH_EXPORT ShelfLayoutManager
   // Overridden from ShellObserver:
   void OnShelfAutoHideBehaviorChanged(WmWindow* root_window) override;
   void OnPinnedStateChanged(WmWindow* pinned_window) override;
+  void OnVirtualKeyboardStateChanged(bool activated,
+                                     WmWindow* root_window) override;
 
   // Overridden from aura::client::ActivationChangeObserver:
   void OnWindowActivated(ActivationReason reason,
@@ -358,6 +365,10 @@ class ASH_EXPORT ShelfLayoutManager
   // MaybeUpdateShelfBackground() instead.
   ShelfBackgroundType shelf_background_type_;
 
+  ScopedObserver<keyboard::KeyboardController,
+                 keyboard::KeyboardControllerObserver>
+      keyboard_observer_;
+
   DISALLOW_COPY_AND_ASSIGN(ShelfLayoutManager);
 };