Fix race condition in media Pipeline::GetMediaTime() after seeking.

media/base/pipeline_impl.cc

Index: media/base/pipeline_impl.cc
diff --git a/media/base/pipeline_impl.cc b/media/base/pipeline_impl.cc
index 85d470a022758459ac8f8f7f7bae599a088d7b76..5dcc4b60ce3c516a29a2d859f1c9edf7c4cfd73f 100644
--- a/media/base/pipeline_impl.cc
+++ b/media/base/pipeline_impl.cc
@@ -958,6 +958,7 @@ void PipelineImpl::Start(Demuxer* demuxer,
   client_ = client;
   seek_cb_ = seek_cb;
   last_media_time_ = base::TimeDelta();
+  pending_seek_time_ = kNoTimestamp;
 
   std::unique_ptr<TextRenderer> text_renderer;
   if (base::CommandLine::ForCurrentProcess()->HasSwitch(
@@ -1039,6 +1040,7 @@ void PipelineImpl::Seek(base::TimeDelta time, const PipelineStatusCB& seek_cb) {
 
   DCHECK(seek_cb_.is_null());
   seek_cb_ = seek_cb;
+  pending_seek_time_ = time;
   last_media_time_ = base::TimeDelta();
   media_task_runner_->PostTask(
       FROM_HERE, base::Bind(&RendererWrapper::Seek,
@@ -1123,7 +1125,11 @@ void PipelineImpl::SetVolume(float volume) {
 base::TimeDelta PipelineImpl::GetMediaTime() const {
   DCHECK(thread_checker_.CalledOnValidThread());
 
-  base::TimeDelta media_time = renderer_wrapper_->GetMediaTime();
+  // Don't trust renderer time during a pending seek. Renderer may return
+  // pre-seek time which may corrupt |last_media_time_| used for clamping.
+  base::TimeDelta media_time = pending_seek_time_ == kNoTimestamp

[sandersd (OOO until July 31), 2017/01/04 21:10:23]

Nit: Swap order.

[chcunningham, 2017/01/04 21:15:46]

Done.

+                                   ? renderer_wrapper_->GetMediaTime()
+                                   : pending_seek_time_;
 
   // Clamp current media time to the last reported value, this prevents higher
   // level clients from seeing time go backwards based on inaccurate or spurious
@@ -1301,6 +1307,8 @@ void PipelineImpl::OnSeekDone() {
   DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(IsRunning());
 
+  pending_seek_time_ = kNoTimestamp;

[chcunningham, 2017/01/04 21:01:37]

Should I also be clearing this in PipelineImp::Resume()? I notice
last_media_time_ is cleared there, but its not obvious why.

[sandersd (OOO until July 31), 2017/01/04 21:10:23]

Resume() should also set the seek time, I believe that OnSeekDone() completes
both operations.

[chcunningham, 2017/01/04 21:15:46]

Done.

+
   DCHECK(!seek_cb_.is_null());
   base::ResetAndReturn(&seek_cb_).Run(PIPELINE_OK);
 }