Fix getUserMedia so that failure is reported for invalid audio sources.

content/renderer/media/external_media_stream_audio_source.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/media/external_media_stream_audio_source.h"
 
 namespace content {
 
 ExternalMediaStreamAudioSource::ExternalMediaStreamAudioSource(
     scoped_refptr<media::AudioCapturerSource> source,
@@ skipping 22 matching lines @@
 bool ExternalMediaStreamAudioSource::EnsureSourceIsStarted() {
   DCHECK(thread_checker_.CalledOnValidThread());
   if (was_started_)
     return true;
   VLOG(1) << "Starting externally-provided "
           << (is_local_source() ? "local" : "remote")
           << " source with audio parameters={"
           << GetAudioParameters().AsHumanReadableString() << "}.";
   source_->Initialize(GetAudioParameters(), this, -1);
   source_->Start();
-  was_started_ = true;
+  // OnCaptureStarted() is expected to be called synchronously by this
+  // implementation. If this needs to be changed, the source needs to be started
+  // outside of EnsureSourceIsStarted since its design is synchronous.
+  CHECK(was_started_);
   return true;
 }
 
 void ExternalMediaStreamAudioSource::EnsureSourceIsStopped() {
   DCHECK(thread_checker_.CalledOnValidThread());
   if (!source_)
     return;
   if (was_started_)
     source_->Stop();
   source_ = nullptr;
   VLOG(1) << "Stopped externally-provided "
           << (is_local_source() ? "local" : "remote")
           << " source with audio parameters={"
           << GetAudioParameters().AsHumanReadableString() << "}.";
 }
 
+void ExternalMediaStreamAudioSource::OnCaptureStarted() {
+  was_started_ = true;
+}
+
 void ExternalMediaStreamAudioSource::Capture(const media::AudioBus* audio_bus,
                                              int audio_delay_milliseconds,
                                              double volume,
                                              bool key_pressed) {
   DCHECK(audio_bus);
   // TODO(miu): Plumbing is needed to determine the actual capture timestamp
   // of the audio, instead of just snapshotting TimeTicks::Now(), for proper
   // audio/video sync. http://crbug.com/335335
   MediaStreamAudioSource::DeliverDataToTracks(
       *audio_bus,
       base::TimeTicks::Now() -
           base::TimeDelta::FromMilliseconds(audio_delay_milliseconds));
 }
 
 void ExternalMediaStreamAudioSource::OnCaptureError(const std::string& why) {
   StopSourceOnError(why);
 }
 
 }  // namespace content