ash: Avoid reloading already-resized custom wallpaper.

ash/desktop_background/wallpaper_resizer.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_DESKTOP_BACKGROUND_DESKTOP_WALLPAPER_RESIZER_H_
 #define ASH_DESKTOP_BACKGROUND_DESKTOP_WALLPAPER_RESIZER_H_
 
 #include "ash/ash_export.h"
 #include "ash/desktop_background/desktop_background_controller.h"
 #include "base/memory/weak_ptr.h"
 #include "base/observer_list.h"
 #include "skia/ext/image_operations.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "ui/gfx/image/image_skia.h"
 #include "ui/gfx/size.h"
 
 namespace ash {
 
 class WallpaperResizerObserver;
 
 // Stores the current wallpaper data and resize it to |target_size| if needed.
 class ASH_EXPORT WallpaperResizer {
  public:
+  // Returns a unique identifier corresponding to |image|, suitable for
+  // comparison against the value returned by original_image_id(). If the image
+  // is modified, its ID will change.
+  static uint32_t GetImageId(const gfx::ImageSkia& image);
+
   WallpaperResizer(int image_resource_id,
                    const gfx::Size& target_size,
                    WallpaperLayout layout);
 
   WallpaperResizer(const gfx::ImageSkia& image,
                    const gfx::Size& target_size,
                    WallpaperLayout layout);
 
   ~WallpaperResizer();
 
-  const gfx::ImageSkia& wallpaper_image() const { return wallpaper_image_; }
-  const WallpaperLayout layout() const { return layout_; }
+  const gfx::ImageSkia& image() const { return image_; }
+  uint32_t original_image_id() const { return original_image_id_; }
+  WallpaperLayout layout() const { return layout_; }
 
   // Called on the UI thread to run Resize() on the worker pool and post an
   // OnResizeFinished() task back to the UI thread on completion.
   void StartResize();
 
   // Add/Remove observers.
   void AddObserver(WallpaperResizerObserver* observer);
   void RemoveObserver(WallpaperResizerObserver* observer);
 
  private:
-  // Copies |resized_bitmap| to |wallpaper_image_| and notifies observers
-  // after Resize() has finished running.
+  // Copies |resized_bitmap| to |image_| and notifies observers after Resize()
+  // has finished running.
   void OnResizeFinished(SkBitmap* resized_bitmap);
 
   ObserverList<WallpaperResizerObserver> observers_;
 
   // Image that should currently be used for wallpaper. It initially
   // contains the original image and is updated to contain the resized
   // image by OnResizeFinished().
-  gfx::ImageSkia wallpaper_image_;
+  gfx::ImageSkia image_;
+
+  // Unique identifier corresponding to the original (i.e. pre-resize) |image_|.
+  uint32_t original_image_id_;
 
   gfx::Size target_size_;
 
   WallpaperLayout layout_;
 
   base::WeakPtrFactory<WallpaperResizer> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(WallpaperResizer);
 };
 
 }  // namespace ash
 
 
 #endif  // ASH_DESKTOP_BACKGROUND_DESKTOP_WALLPAPER_RESIZER_H_