MediaStream audio: Refactor 3 separate "glue" implementations into one.

content/renderer/media/external_media_stream_audio_source.h

Index: content/renderer/media/external_media_stream_audio_source.h
diff --git a/content/renderer/media/external_media_stream_audio_source.h b/content/renderer/media/external_media_stream_audio_source.h
new file mode 100644
index 0000000000000000000000000000000000000000..f520ae0985abb145ce8bcb3e2a353e91ee360f93
--- /dev/null
+++ b/content/renderer/media/external_media_stream_audio_source.h
@@ -0,0 +1,59 @@
+// 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.
+
+#ifndef CONTENT_RENDERER_MEDIA_EXTERNAL_MEDIA_STREAM_AUDIO_SOURCE_H_
+#define CONTENT_RENDERER_MEDIA_EXTERNAL_MEDIA_STREAM_AUDIO_SOURCE_H_
+
+#include "content/renderer/media/media_stream_audio_source.h"
+
+#include "media/base/audio_capturer_source.h"
+
+namespace content {
+
+// Represents an externally-provided local or remote source of audio data. This
+// allows users of the public content::MediaStreamApi to provide a
+// media::AudioCapturerSource to be used as the source of audio data in the
+// MediaStream framework. Audio data is transported directly to the tracks
+// (i.e., there is no audio processing).
+class CONTENT_EXPORT ExternalMediaStreamAudioSource final
+    : NON_EXPORTED_BASE(public MediaStreamAudioSource),
+      NON_EXPORTED_BASE(public media::AudioCapturerSource::CaptureCallback) {
+ public:
+  ExternalMediaStreamAudioSource(
+      scoped_refptr<media::AudioCapturerSource> source,
+      int sample_rate,
+      media::ChannelLayout channel_layout,
+      int frames_per_buffer,
+      bool is_remote);
+
+  ~ExternalMediaStreamAudioSource() final;
+
+ private:
+  // MediaStreamAudioSource implementation.
+  bool EnsureSourceIsStarted() final;
+  void EnsureSourceIsStopped() final;
+
+  // media::AudioCapturerSource::CaptureCallback implementation.
+  void Capture(const media::AudioBus* audio_bus,
+               int audio_delay_milliseconds,
+               double volume,
+               bool key_pressed) final;
+  void OnCaptureError(const std::string& message) final;
+
+  // The external source provided to the constructor.
+  scoped_refptr<media::AudioCapturerSource> source_;
+
+  // In debug builds, check that all methods that could cause object graph
+  // or data flow changes are being called on the main thread.
+  base::ThreadChecker thread_checker_;
+
+  // True once the source has been started successfully.
+  bool was_started_;
+
+  DISALLOW_COPY_AND_ASSIGN(ExternalMediaStreamAudioSource);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_MEDIA_EXTERNAL_MEDIA_STREAM_AUDIO_SOURCE_H_