Add support for cancellation of demuxer reads.

media/blink/multibuffer_data_source.cc

Index: media/blink/multibuffer_data_source.cc
diff --git a/media/blink/multibuffer_data_source.cc b/media/blink/multibuffer_data_source.cc
index 494ea264664aeaa3e005922b02633ae8b58e0bfd..9696558f077cbaca9e291ee9b9108aafb443cf83 100644
--- a/media/blink/multibuffer_data_source.cc
+++ b/media/blink/multibuffer_data_source.cc
@@ -263,16 +263,6 @@ bool MultibufferDataSource::DidPassCORSAccessCheck() const {
   return true;
 }
 
-void MultibufferDataSource::Abort() {
-  DCHECK(render_task_runner_->BelongsToCurrentThread());
-  {
-    base::AutoLock auto_lock(lock_);
-    StopInternal_Locked();
-  }
-  StopLoader();
-  frame_ = NULL;
-}
-
 void MultibufferDataSource::MediaPlaybackRateChanged(double playback_rate) {
   DCHECK(render_task_runner_->BelongsToCurrentThread());
   DCHECK(reader_.get());
@@ -307,6 +297,13 @@ void MultibufferDataSource::Stop() {
                                            weak_factory_.GetWeakPtr()));
 }
 
+void MultibufferDataSource::Abort() {

[hubbe, 2016/08/24 23:39:43]

DCHECK() that we're on the right thread?

[DaleCurtis, 2016/08/24 23:41:10]

Other data source operations are not DCHECK'd since they happen on the media
thread and not the |render_task_runner_|.

[hubbe, 2016/08/24 23:43:29]

The previous Abort() had a DCHECK(), unless you're intending to call this from
multiple different threads, I think we need to keep that.

[DaleCurtis, 2016/08/24 23:49:41]

The previous Abort() method was dead code :) 

+  base::AutoLock auto_lock(lock_);
+  DCHECK(init_cb_.is_null());
+  if (read_op_)
+    ReadOperation::Run(std::move(read_op_), kReadError);
+}
+
 void MultibufferDataSource::SetBitrate(int bitrate) {
   render_task_runner_->PostTask(
       FROM_HERE, base::Bind(&MultibufferDataSource::SetBitrateTask,