ash: Start/stop observing KeyboardController via ShellObserver

ash/common/wm/workspace/workspace_layout_manager.h

Index: ash/common/wm/workspace/workspace_layout_manager.h
diff --git a/ash/common/wm/workspace/workspace_layout_manager.h b/ash/common/wm/workspace/workspace_layout_manager.h
index af7d795d69e05e309242b47f13fc3a9e0d0d3a36..3f3ac672ce5a0c4ae5454f9f5812017b613f9d62 100644
--- a/ash/common/wm/workspace/workspace_layout_manager.h
+++ b/ash/common/wm/workspace/workspace_layout_manager.h
@@ -14,12 +14,17 @@
 #include "ash/common/wm/wm_types.h"
 #include "ash/common/wm_layout_manager.h"
 #include "base/macros.h"
+#include "base/scoped_observer.h"
 #include "ui/aura/window_observer.h"
 #include "ui/display/display_observer.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 ash {
 
 class RootWindowController;
@@ -92,6 +97,8 @@ class ASH_EXPORT WorkspaceLayoutManager
   void OnFullscreenStateChanged(bool is_fullscreen,
                                 WmWindow* root_window) override;
   void OnPinnedStateChanged(WmWindow* pinned_window) override;
+  void OnVirtualKeyboardStateChanged(bool activated,
+                                     WmWindow* root_window) override;
 
  private:
   typedef std::set<WmWindow*> WindowSet;
@@ -134,6 +141,10 @@ class ASH_EXPORT WorkspaceLayoutManager
   // topmost visible window.
   std::unique_ptr<WorkspaceLayoutManagerBackdropDelegate> backdrop_delegate_;
 
+  ScopedObserver<keyboard::KeyboardController,
+                 keyboard::KeyboardControllerObserver>
+      keyboard_observer_;
+
   DISALLOW_COPY_AND_ASSIGN(WorkspaceLayoutManager);
 };