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

chrome/browser/chromeos/arc/arc_wallpaper_handler.h

Index: chrome/browser/chromeos/arc/arc_wallpaper_handler.h
diff --git a/chrome/browser/chromeos/arc/arc_wallpaper_handler.h b/chrome/browser/chromeos/arc/arc_wallpaper_handler.h
index cb4b96d65158066d7d6720de953a5c58bb00b389..8051b8578a41418d28413faf997f3d74c1b2a3be 100644
--- a/chrome/browser/chromeos/arc/arc_wallpaper_handler.h
+++ b/chrome/browser/chromeos/arc/arc_wallpaper_handler.h
@@ -31,11 +31,14 @@ class ArcWallpaperHandler : public SetWallpaperDelegate {
   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);
 };