Fix login visual hitch on chromebook

chrome/browser/image_decoder.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 CHROME_BROWSER_IMAGE_DECODER_H_
 #define CHROME_BROWSER_IMAGE_DECODER_H_
 
 #include <string>
 #include <vector>
 
 #include "base/compiler_specific.h"
+#include "base/threading/sequenced_worker_pool.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/utility_process_host_client.h"
 
 class SkBitmap;
 
 // Decodes an image in a sandboxed process.
 class ImageDecoder : public content::UtilityProcessHostClient {
  public:
   class Delegate {
    public:
@@ skipping 13 matching lines @@
 
   enum ImageCodec {
     DEFAULT_CODEC = 0,  // Uses WebKit image decoding (via WebImage).
     ROBUST_JPEG_CODEC,  // Restrict decoding to robust jpeg codec.
   };
 
   ImageDecoder(Delegate* delegate,
                const std::string& image_data,
                ImageCodec image_codec);
 
-  // Starts image decoding.
+  // Starts image decoding on well-known threads.
   void Start();
 
+  // Starts image decoding on a sequence worker thread with a sequence token
+  // |sequence_token|.
+  void Start(const base::SequencedWorkerPool::SequenceToken& sequence_token);
+
   const std::vector<unsigned char>& get_image_data() const {
     return image_data_;
   }
 
   void set_delegate(Delegate* delegate) { delegate_ = delegate; }
 
  private:
   // It's a reference counted object, so destructor is private.
   virtual ~ImageDecoder();
 
   // Overidden from UtilityProcessHostClient:
   virtual bool OnMessageReceived(const IPC::Message& message) OVERRIDE;
 
+  // True if on valid thread or named worker thread associated with
+  // |sequence_token_name_|.
+  bool CalledOnValidThreadOrWorkerThread();
+
   // IPC message handlers.
   void OnDecodeImageSucceeded(const SkBitmap& decoded_image);
   void OnDecodeImageFailed();
 
   // Launches sandboxed process that will decode the image.
   void DecodeImageInSandbox(const std::vector<unsigned char>& image_data);
 
   Delegate* delegate_;
   std::vector<unsigned char> image_data_;
   const ImageCodec image_codec_;
   content::BrowserThread::ID target_thread_id_;
+  base::SequencedWorkerPool::SequenceToken sequence_token_;
+  bool decode_on_sequence_worker_thread_;
 
   DISALLOW_COPY_AND_ASSIGN(ImageDecoder);
 };
 
 #endif  // CHROME_BROWSER_IMAGE_DECODER_H_