Fix login visual hitch on chromebook

chrome/browser/chromeos/login/user_image_loader.h

Index: chrome/browser/chromeos/login/user_image_loader.h
diff --git a/chrome/browser/chromeos/login/user_image_loader.h b/chrome/browser/chromeos/login/user_image_loader.h
index a5a8b4589c29016c79a2a2b9351f7516f923e010..e07760056cea9b752c9e53413760a460d9b0ff6f 100644
--- a/chrome/browser/chromeos/login/user_image_loader.h
+++ b/chrome/browser/chromeos/login/user_image_loader.h
@@ -11,6 +11,8 @@
 #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;
@@ -28,6 +30,8 @@ class UserImageLoader : public base::RefCountedThreadSafe<UserImageLoader>,
   // Callback used to indicate that image has been loaded.
   typedef base::Callback<void(const UserImage& user_image)> LoadedCallback;
 
+  typedef base::SequencedWorkerPool::SequenceToken SequenceToken;
+
   explicit UserImageLoader(ImageDecoder::ImageCodec image_codec);
 
   // Start reading the image from |filepath| on the file thread. Calls
@@ -55,7 +59,9 @@ class UserImageLoader : public base::RefCountedThreadSafe<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);
+  void LoadImage(const std::string& filepath,
+                 const ImageInfo& image_info,
+                 const SequenceToken& sequence_token);
 
   // ImageDecoder::Delegate implementation.
   virtual void OnImageDecoded(const ImageDecoder* decoder,
@@ -68,6 +74,9 @@ class UserImageLoader : public base::RefCountedThreadSafe<UserImageLoader>,
   // 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.
   ImageInfoMap image_info_map_;