Add WorkspaceObserver to observe changes in workspace state

ui/aura_shell/workspace/workspace_controller.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/aura_shell/workspace/workspace_controller.h"
 
 #include "ui/aura/desktop.h"
 #include "ui/aura/window.h"
 #include "ui/aura_shell/default_container_layout_manager.h"
 #include "ui/aura_shell/workspace/workspace.h"
 #include "ui/aura_shell/workspace/workspace_manager.h"
 
 namespace aura_shell {
 namespace internal {
 
-WorkspaceController::WorkspaceController(aura::Window* window)
-    : workspace_manager_(new WorkspaceManager(window)),
-      layout_manager_(new internal::DefaultContainerLayoutManager(
-          window, workspace_manager_.get())) {
-  window->SetLayoutManager(layout_manager_);
+WorkspaceController::WorkspaceController(aura::Window* viewport)
+    : workspace_manager_(new WorkspaceManager(viewport)) {
   aura::Desktop::GetInstance()->AddObserver(this);
 }
 
 WorkspaceController::~WorkspaceController() {
   aura::Desktop::GetInstance()->RemoveObserver(this);
 }
 
 void WorkspaceController::ToggleOverview() {
   workspace_manager_->SetOverview(!workspace_manager_->is_overview());
 }
 
 void WorkspaceController::OnDesktopResized(const gfx::Size& new_size) {
-  layout_manager_->set_ignore_calculate_bounds(true);
   workspace_manager_->SetWorkspaceSize(new_size);
-  layout_manager_->set_ignore_calculate_bounds(false);
 }
 
 void WorkspaceController::OnActiveWindowChanged(aura::Window* active) {
   // FindBy handles NULL.
   Workspace* workspace = workspace_manager_->FindBy(active);
   if (workspace)
     workspace->Activate();
 }
 
 }  // namespace internal
 }  // namespace aura_shell