Add WorkspaceObserver to observe changes in workspace state

ui/aura_shell/workspace/workspace_controller.h

Index: ui/aura_shell/workspace/workspace_controller.h
diff --git a/ui/aura_shell/workspace/workspace_controller.h b/ui/aura_shell/workspace/workspace_controller.h
index d928f96db10126756e7639d6318c1f2103b08138..5e9ff86e6a8a2a50c6ce45514a17c18b99590c44 100644
--- a/ui/aura_shell/workspace/workspace_controller.h
+++ b/ui/aura_shell/workspace/workspace_controller.h
@@ -28,13 +28,14 @@ class WorkspaceManager;
 // events From DesktopObserver translating them to WorkspaceManager.
 class AURA_SHELL_EXPORT WorkspaceController : public aura::DesktopObserver {
  public:
-  explicit WorkspaceController(aura::Window* window);
+  explicit WorkspaceController(aura::Window* workspace_viewport);
   virtual ~WorkspaceController();
 
   void ToggleOverview();
 
-  internal::DefaultContainerLayoutManager* layout_manager() {
-    return layout_manager_;
+  // Returns the workspace manager that this controler owns.
+  WorkspaceManager* workspace_manager() {
+    return workspace_manager_.get();
   }
 
   // DesktopObserver overrides:
@@ -44,9 +45,6 @@ class AURA_SHELL_EXPORT WorkspaceController : public aura::DesktopObserver {
  private:
   scoped_ptr<WorkspaceManager> workspace_manager_;
 
-  // This is owned by the window it's installed on.
-  internal::DefaultContainerLayoutManager* layout_manager_;
-
   DISALLOW_COPY_AND_ASSIGN(WorkspaceController);
 };