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

content/renderer/media/external_media_stream_audio_source.h

 // 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_BROWSER_DEVICE_SENSORS_DEVICE_SENSOR_MESSAGE_FILTER_H_
-#define CONTENT_BROWSER_DEVICE_SENSORS_DEVICE_SENSOR_MESSAGE_FILTER_H_
+#ifndef CONTENT_RENDERER_MEDIA_EXTERNAL_MEDIA_STREAM_AUDIO_SOURCE_H_
+#define CONTENT_RENDERER_MEDIA_EXTERNAL_MEDIA_STREAM_AUDIO_SOURCE_H_
 
-#include "base/macros.h"
-#include "base/memory/shared_memory.h"
-#include "content/browser/device_sensors/device_sensors_consts.h"
-#include "content/public/browser/browser_message_filter.h"
+#include "content/renderer/media/media_stream_audio_source.h"
+
+#include "media/base/audio_capturer_source.h"
 
 namespace content {
 
-// A base class for device sensor related message filters.
-class DeviceSensorMessageFilter : public BrowserMessageFilter {
+// 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:
-  DeviceSensorMessageFilter(ConsumerType consumer_type,
-                            uint32_t message_class_to_filter);
+  ExternalMediaStreamAudioSource(
+      scoped_refptr<media::AudioCapturerSource> source,
+      int sample_rate,
+      media::ChannelLayout channel_layout,
+      int frames_per_buffer,
+      bool is_remote);
 
- protected:
-  // All methods below to be called on the IO thread.
-  ~DeviceSensorMessageFilter() override;
-
-  virtual void OnStartPolling();
-  virtual void OnStopPolling();
-  // To be overriden by the subclass in order to send the appropriate message
-  // to the renderer with a handle to shared memory.
-  virtual void DidStartPolling(base::SharedMemoryHandle handle) = 0;
+  ~ExternalMediaStreamAudioSource() final;
 
  private:
-  ConsumerType consumer_type_;
+  // MediaStreamAudioSource implementation.
+  void DoStopSource() final;
+  bool EnsureSourceIsStarted() 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.
+  const scoped_refptr<media::AudioCapturerSource> source_;
+
+  // True once the source has been started successfully.
   bool is_started_;
 
-  DISALLOW_COPY_AND_ASSIGN(DeviceSensorMessageFilter);
+  DISALLOW_COPY_AND_ASSIGN(ExternalMediaStreamAudioSource);
 };
 
 }  // namespace content
 
-#endif  // CONTENT_BROWSER_DEVICE_SENSORS_DEVICE_SENSOR_MESSAGE_FILTER_H_
+#endif  // CONTENT_RENDERER_MEDIA_EXTERNAL_MEDIA_STREAM_AUDIO_SOURCE_H_