Rename ash desktop_background to wallpaper.

ash/wm/system_wallpaper_controller.h

 // Copyright (c) 2012 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_SYSTEM_BACKGROUND_CONTROLLER_H_
-#define ASH_WM_SYSTEM_BACKGROUND_CONTROLLER_H_
+#ifndef ASH_WM_SYSTEM_WALLPAPER_CONTROLLER_H_
+#define ASH_WM_SYSTEM_WALLPAPER_CONTROLLER_H_
 
 #include <memory>
 #include <string>
 
 #include "ash/ash_export.h"
 #include "base/macros.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/aura/window_observer.h"
 
 namespace ui {
 class Layer;
 }
 
 namespace ash {
 
-// SystemBackgroundController manages a ui::Layer that's stacked at the bottom
+// SystemWallpaperController manages a ui::Layer that's stacked at the bottom
 // of an aura::RootWindow's children.  It exists solely to obscure portions of
 // the root layer that aren't covered by any other layers (e.g. before the
-// desktop background image is loaded at startup, or when we scale down all of
-// the other layers as part of a power-button or window-management animation).
+// wallpaper image is loaded at startup, or when we scale down all of the other
+// layers as part of a power-button or window-management animation).
 // It should never be transformed or restacked.
-class SystemBackgroundController : public aura::WindowObserver {
+class SystemWallpaperController : public aura::WindowObserver {
  public:
-  SystemBackgroundController(aura::Window* root_window, SkColor color);
-  ~SystemBackgroundController() override;
+  SystemWallpaperController(aura::Window* root_window, SkColor color);
+  ~SystemWallpaperController() override;
 
   void SetColor(SkColor color);
 
   // aura::WindowObserver overrides:
   void OnWindowBoundsChanged(aura::Window* root,
                              const gfx::Rect& old_bounds,
                              const gfx::Rect& new_bounds) override;
 
  private:
   class HostContentLayerDelegate;
 
   aura::Window* root_window_;  // not owned
 
   std::unique_ptr<ui::Layer> layer_;
 
-  DISALLOW_COPY_AND_ASSIGN(SystemBackgroundController);
+  DISALLOW_COPY_AND_ASSIGN(SystemWallpaperController);
 };
 
 }  // namespace ash
 
-#endif  // ASH_WM_SYSTEM_BACKGROUND_CONTROLLER_H_
+#endif  // ASH_WM_SYSTEM_WALLPAPER_CONTROLLER_H_