Fix login visual hitch on chromebook

chrome/browser/image_decoder.cc

Index: chrome/browser/image_decoder.cc
diff --git a/chrome/browser/image_decoder.cc b/chrome/browser/image_decoder.cc
index 6d7b948aa7f63a79dc817fc41088aec47cd588d3..682789f9c6af128183a5d1c9b6b7bc16f84268ca 100644
--- a/chrome/browser/image_decoder.cc
+++ b/chrome/browser/image_decoder.cc
@@ -5,6 +5,7 @@
 #include "chrome/browser/image_decoder.h"
 
 #include "base/bind.h"
+#include "base/threading/sequenced_worker_pool.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/common/chrome_utility_messages.h"
 #include "content/public/browser/browser_thread.h"
@@ -34,6 +35,17 @@ void ImageDecoder::Start() {
      base::Bind(&ImageDecoder::DecodeImageInSandbox, this, image_data_));
 }
 
+void ImageDecoder::Start(std::string sequence_token_name) {
+  if (sequence_token_name.empty()) {
+    NOTREACHED();
+    return;
+  }
+  sequence_token_name_ = sequence_token_name;
+  BrowserThread::PostTask(
+     BrowserThread::IO, FROM_HERE,
+     base::Bind(&ImageDecoder::DecodeImageInSandbox, this, image_data_));
+}
+
 bool ImageDecoder::OnMessageReceived(const IPC::Message& message) {
   bool handled = true;
   IPC_BEGIN_MESSAGE_MAP(ImageDecoder, message)
@@ -46,14 +58,25 @@ bool ImageDecoder::OnMessageReceived(const IPC::Message& message) {
   return handled;
 }
 
+bool ImageDecoder::CalledOnValidThreadOrWorkerThread() {
+  if (sequence_token_name_.empty()) {
+    return BrowserThread::CurrentlyOn(target_thread_id_);
+  } else {
+    base::SequencedWorkerPool* pool = BrowserThread::GetBlockingPool();
+    base::SequencedWorkerPool::SequenceToken sequence_token = pool->
+        GetNamedSequenceToken(sequence_token_name_);
+    return pool->IsRunningSequenceOnCurrentThread(sequence_token);
+  }
+}
+
 void ImageDecoder::OnDecodeImageSucceeded(const SkBitmap& decoded_image) {
-  DCHECK(BrowserThread::CurrentlyOn(target_thread_id_));
+  DCHECK(CalledOnValidThreadOrWorkerThread());
   if (delegate_)
     delegate_->OnImageDecoded(this, decoded_image);
 }
 
 void ImageDecoder::OnDecodeImageFailed() {
-  DCHECK(BrowserThread::CurrentlyOn(target_thread_id_));
+  DCHECK(CalledOnValidThreadOrWorkerThread());
   if (delegate_)
     delegate_->OnDecodeImageFailed(this);
 }
@@ -61,8 +84,17 @@ void ImageDecoder::OnDecodeImageFailed() {
 void ImageDecoder::DecodeImageInSandbox(
     const std::vector<unsigned char>& image_data) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  UtilityProcessHost* utility_process_host = UtilityProcessHost::Create(
-      this, BrowserThread::GetMessageLoopProxyForThread(target_thread_id_));
+  UtilityProcessHost* utility_process_host;
+  if (sequence_token_name_.empty()) {
+    utility_process_host = UtilityProcessHost::Create(
+        this, BrowserThread::GetMessageLoopProxyForThread(target_thread_id_));
+  } else {
+    base::SequencedWorkerPool* pool = BrowserThread::GetBlockingPool();
+    base::SequencedWorkerPool::SequenceToken sequence_token = pool->
+        GetNamedSequenceToken(sequence_token_name_);
+    utility_process_host = UtilityProcessHost::Create(
+        this, pool->GetSequencedTaskRunner(sequence_token).get());
+  }
   utility_process_host->EnableZygote();
   if (image_codec_ == ROBUST_JPEG_CODEC) {
     utility_process_host->Send(