Revert of Only create DockedBackgroundWidget as needed.

ash/wm/dock/docked_window_layout_manager.h

 // Copyright (c) 2013 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.
 
 #ifndef ASH_WM_DOCK_DOCKED_WINDOW_LAYOUT_MANAGER_H_
 #define ASH_WM_DOCK_DOCKED_WINDOW_LAYOUT_MANAGER_H_
 
 #include <memory>
 
 #include "ash/ash_export.h"
+#include "ash/shelf/shelf_layout_manager_observer.h"
 #include "ash/shell_observer.h"
 #include "ash/snap_to_pixel_layout_manager.h"
 #include "ash/wm/dock/dock_types.h"
 #include "ash/wm/dock/docked_window_layout_manager_observer.h"
 #include "ash/wm/window_state_observer.h"
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/observer_list.h"
 #include "base/time/time.h"
 #include "ui/aura/window.h"
@@ skipping 12 matching lines @@
 
 namespace views {
 class Widget;
 }
 
 namespace ash {
 class DockedBackgroundWidget;
 class DockedWindowLayoutManagerObserver;
 class DockedWindowResizerTest;
 class Shelf;
+class ShelfLayoutManager;
 class WorkspaceController;
 
 struct WindowWithHeight {
   explicit WindowWithHeight(aura::Window* window) :
     window_(window),
     height_(window->bounds().height()) { }
   aura::Window* window() { return window_; }
   const aura::Window* window() const { return window_; }
   aura::Window* window_;
   int height_;
@@ skipping 10 matching lines @@
 //     new DockedWindowLayoutManager(dock_container));
 //
 // TODO(varkha): extend BaseLayoutManager instead of LayoutManager to inherit
 // common functionality.
 class ASH_EXPORT DockedWindowLayoutManager
     : public SnapToPixelLayoutManager,
       public ash::ShellObserver,
       public aura::WindowObserver,
       public aura::client::ActivationChangeObserver,
       public keyboard::KeyboardControllerObserver,
+      public ShelfLayoutManagerObserver,
       public wm::WindowStateObserver {
  public:
   // Maximum width of the docked windows area.
   static const int kMaxDockWidth;
 
   // Minimum width of the docked windows area.
   static const int kMinDockWidth;
 
   DockedWindowLayoutManager(aura::Window* dock_container,
                             WorkspaceController* workspace_controller);
@@ skipping 70 matching lines @@
                                       bool visibile) override;
   void SetChildBounds(aura::Window* child,
                       const gfx::Rect& requested_bounds) override;
 
   // ash::ShellObserver:
   void OnDisplayWorkAreaInsetsChanged() override;
   void OnFullscreenStateChanged(bool is_fullscreen,
                                 aura::Window* root_window) override;
   void OnShelfAlignmentChanged(aura::Window* root_window) override;
 
+  // ShelfLayoutManagerObserver:
+  void OnBackgroundUpdated(ShelfBackgroundType background_type,
+                           BackgroundAnimatorChangeType change_type) override;
+
   // wm::WindowStateObserver:
   void OnPreWindowStateTypeChange(wm::WindowState* window_state,
                                   wm::WindowStateType old_type) override;
 
   // aura::WindowObserver:
   void OnWindowBoundsChanged(aura::Window* window,
                              const gfx::Rect& old_bounds,
                              const gfx::Rect& new_bounds) override;
   void OnWindowVisibilityChanging(aura::Window* window, bool visible) override;
   void OnWindowDestroying(aura::Window* window) override;
@@ skipping 147 matching lines @@
 
   // Observers of dock bounds changes.
   base::ObserverList<DockedWindowLayoutManagerObserver> observer_list_;
 
   DISALLOW_COPY_AND_ASSIGN(DockedWindowLayoutManager);
 };
 
 }  // namespace ash
 
 #endif  // ASH_WM_DOCK_DOCKED_WINDOW_LAYOUT_MANAGER_H_