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..3b166606887fe2e4969aae4bc366cd76e29dd1e0 100644
--- a/chrome/browser/image_decoder.cc
+++ b/chrome/browser/image_decoder.cc
@@ -19,12 +19,14 @@ ImageDecoder::ImageDecoder(Delegate* delegate,
     : delegate_(delegate),
       image_data_(image_data.begin(), image_data.end()),
       image_codec_(image_codec),
-      target_thread_id_(BrowserThread::UI) {
+      target_thread_id_(BrowserThread::UI),
+      decode_on_sequence_worker_thread_(false) {
 }
 
 ImageDecoder::~ImageDecoder() {}
 
 void ImageDecoder::Start() {
+  decode_on_sequence_worker_thread_ = false;
   if (!BrowserThread::GetCurrentThreadIdentifier(&target_thread_id_)) {
     NOTREACHED();
     return;
@@ -34,6 +36,15 @@ void ImageDecoder::Start() {
      base::Bind(&ImageDecoder::DecodeImageInSandbox, this, image_data_));
 }
 
+void ImageDecoder::Start(
+    const base::SequencedWorkerPool::SequenceToken& sequence_token) {

[Joao da Silva, 2013/01/21 08:07:39]

Why not have a single Start() that gets a TaskRunner?

The 1st version is invoked as

base::TaskRunner* task_runner =
    BrowserThread::GetMessageLoopProxyForThread(BrowserThread::FILE);
decoder->Start(task_runner);

and the 2nd:

base::TaskRunner* task_runner =
    BrowserThread::GetBlockingPool()->GetSequencedTaskRunner(sequence_token);
decoder->Start(task_runner);


CalledOnValidThreadOrWorkerThread() then just becomes:
task_runner_->RunsTasksOnCurrentThread()

[bshe, 2013/01/21 22:53:07]

Good idea!
We only have one Start function now.

On 2013/01/21 08:07:39, Joao da Silva wrote:

+  sequence_token_ = sequence_token;
+  decode_on_sequence_worker_thread_ = true;
+  BrowserThread::PostTask(
+     BrowserThread::IO, FROM_HERE,
+     base::Bind(&ImageDecoder::DecodeImageInSandbox, this, image_data_));

[Joao da Silva, 2013/01/21 08:07:39]

nit: indent (4 spaces)

[bshe, 2013/01/21 22:53:07]

This is an argument of function PostTask, same as BrowserThread::IO. I remember
the arguments should be aligned in this case.
http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml?showone=Functi...
 
Or maybe I understood it wrong?

 
On 2013/01/21 08:07:39, Joao da Silva wrote:

+}
+
 bool ImageDecoder::OnMessageReceived(const IPC::Message& message) {
   bool handled = true;
   IPC_BEGIN_MESSAGE_MAP(ImageDecoder, message)
@@ -46,14 +57,23 @@ bool ImageDecoder::OnMessageReceived(const IPC::Message& message) {
   return handled;
 }
 
+bool ImageDecoder::CalledOnValidThreadOrWorkerThread() {
+  if (decode_on_sequence_worker_thread_) {
+    return BrowserThread::GetBlockingPool()->
+        IsRunningSequenceOnCurrentThread(sequence_token_);
+  } else {
+    return BrowserThread::CurrentlyOn(target_thread_id_);
+  }
+}
+
 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 +81,15 @@ 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 (decode_on_sequence_worker_thread_) {
+    utility_process_host = UtilityProcessHost::Create(
+        this, BrowserThread::GetBlockingPool()->GetSequencedTaskRunner(
+            sequence_token_).get());
+  } else {
+    utility_process_host = UtilityProcessHost::Create(
+        this, BrowserThread::GetMessageLoopProxyForThread(target_thread_id_));
+  }
   utility_process_host->EnableZygote();
   if (image_codec_ == ROBUST_JPEG_CODEC) {
     utility_process_host->Send(