Fix login visual hitch on chromebook

chrome/browser/chromeos/login/user_image_loader.h

-// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// 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 CHROME_BROWSER_CHROMEOS_LOGIN_USER_IMAGE_LOADER_H_
 #define CHROME_BROWSER_CHROMEOS_LOGIN_USER_IMAGE_LOADER_H_
 
 #include <map>
 #include <string>
 
 #include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/memory/ref_counted.h"
+#include "base/synchronization/lock.h"
+#include "base/threading/sequenced_worker_pool.h"
 #include "chrome/browser/image_decoder.h"
 
 class MessageLoop;
 class SkBitmap;
 
 namespace chromeos {
 
 class UserImage;
 
 // A facility to read a file containing user image asynchronously in the IO
 // thread. Returns the image in the form of an SkBitmap.
 class UserImageLoader : public base::RefCountedThreadSafe<UserImageLoader>,
                         public ImageDecoder::Delegate {
  public:
   // Callback used to indicate that image has been loaded.
   typedef base::Callback<void(const UserImage& user_image)> LoadedCallback;
 
   explicit UserImageLoader(ImageDecoder::ImageCodec image_codec);
 
-  // Start reading the image from |filepath| on the file thread. Calls
+  // Start reading the image from |filepath| on a worker thread pool. Calls
   // |loaded_cb| when image has been successfully loaded.
   // If |size| is positive, image is cropped and (if needed) downsized to
   // |size|x|size| pixels.
   void Start(const std::string& filepath, int size,
              const LoadedCallback& loaded_cb);
 
  private:
   friend class base::RefCountedThreadSafe<UserImageLoader>;
 
   // Contains attributes we need to know about each image we decode.
   struct ImageInfo {
     ImageInfo(int size, const LoadedCallback& loaded_cb);
     ~ImageInfo();
 
     const int size;
     const LoadedCallback loaded_cb;
   };
 
   typedef std::map<const ImageDecoder*, ImageInfo> ImageInfoMap;
 
   virtual ~UserImageLoader();
 
-  // Method that reads the file on the file thread and starts decoding it in
-  // sandboxed process.
-  void LoadImage(const std::string& filepath, const ImageInfo& image_info);
+  // Method that reads the file on the worker thread pool and starts decoding it
+  // in a sandboxed process.
+  void LoadImage(const std::string& filepath,
+                 const ImageInfo& image_info,
+                 scoped_refptr<base::SequencedTaskRunner> task_runner);
 
   // ImageDecoder::Delegate implementation.
   virtual void OnImageDecoded(const ImageDecoder* decoder,
                               const SkBitmap& decoded_image) OVERRIDE;
   virtual void OnDecodeImageFailed(const ImageDecoder* decoder) OVERRIDE;
 
   // The message loop object of the thread in which we notify the delegate.
   MessageLoop* target_message_loop_;
 
   // Specify how the file should be decoded in the utility process.
   const ImageDecoder::ImageCodec image_codec_;
 
+  // Proctect image_info_map_
+  base::Lock lock_;
+
   // Holds info structures about all images we're trying to decode.
-  // Accessed only on FILE thread.
+  // Accessed on multiple worker threads.
   ImageInfoMap image_info_map_;
 
   DISALLOW_COPY_AND_ASSIGN(UserImageLoader);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_LOGIN_USER_IMAGE_LOADER_H_