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..a1a3020d6010e73d9cd19d90ec5bbd7f779b5b28 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() {
+  base::AutoLock auto_lock(lock_);
+  DCHECK(init_cb_.is_null());
+  if (read_op_)
+    ReadOperation::Run(std::move(read_op_), kAborted);
+}
+
 void MultibufferDataSource::SetBitrate(int bitrate) {
   render_task_runner_->PostTask(
       FROM_HERE, base::Bind(&MultibufferDataSource::SetBitrateTask,
@@ -380,9 +377,8 @@ void MultibufferDataSource::ReadTask() {
 
   base::AutoLock auto_lock(lock_);
   int bytes_read = 0;
-  if (stop_signal_received_)
+  if (stop_signal_received_ || !read_op_)
     return;
-  DCHECK(read_op_);
   DCHECK(read_op_->size());
 
   if (!reader_) {