arc: Do not keep track of in-flight decode requests.

chrome/browser/chromeos/arc/arc_wallpaper_handler.h

 // Copyright 2016 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 CHROME_BROWSER_CHROMEOS_ARC_ARC_WALLPAPER_HANDLER_H_
 #define CHROME_BROWSER_CHROMEOS_ARC_ARC_WALLPAPER_HANDLER_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 13 matching lines @@
   ArcWallpaperHandler();
   ~ArcWallpaperHandler() override;
 
   // SetWallpaperDelegate implementation.
   void SetWallpaper(const std::vector<uint8_t>& jpeg_data) override;
 
  private:
   class ImageRequestImpl;
 
   // Called from ImageRequestImpl on decode completion.
-  void OnImageDecoded(ImageRequestImpl* request, const SkBitmap& bitmap);
-  void OnDecodeImageFailed(ImageRequestImpl* request);
+  void OnImageDecoded(const SkBitmap& bitmap);
+  void OnDecodeImageFailed();
 
-  // The set of in-flight decode requests.
-  std::set<std::unique_ptr<ImageRequestImpl>> inflight_requests_;
+  // Cancel the in-flight request if any.
+  void CancelInflightRequest();
+
+  // The in-flight decode request.
+  std::unique_ptr<ImageRequestImpl> inflight_request_;
 
   DISALLOW_COPY_AND_ASSIGN(ArcWallpaperHandler);
 };
 
 }  // namespace arc
 
 #endif  // CHROME_BROWSER_CHROMEOS_ARC_ARC_WALLPAPER_HANDLER_H_