MediaCaptureFromElement: add support for audio captureStream().

content/renderer/media/html_audio_element_capturer_source.h

Index: content/renderer/media/html_audio_element_capturer_source.h
diff --git a/content/renderer/media/html_audio_element_capturer_source.h b/content/renderer/media/html_audio_element_capturer_source.h
new file mode 100644
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+++ b/content/renderer/media/html_audio_element_capturer_source.h
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+// 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_HTML_AUDIO_ELEMENT_CAPTURER_SOURCE_H_
+#define CONTENT_RENDERER_MEDIA_HTML_AUDIO_ELEMENT_CAPTURER_SOURCE_H_
+
+#include "base/callback.h"
+#include "base/memory/weak_ptr.h"
+#include "base/threading/thread_checker.h"
+#include "content/common/content_export.h"
+#include "content/renderer/media/media_stream_audio_source.h"
+
+namespace blink {
+class WebMediaPlayer;
+}  // namespace blink
+
+namespace media {
+class AudioBus;
+class WebAudioSourceProviderImpl;
+}  // namespace media
+
+namespace content {
+
+// This class is a MediaStreamAudioSource that registers to the constructor-
+// passed weak WebAudioSourceProviderImpl to receive a copy of the audio data
+// intended for rendering. This copied data is received on OnAudioBus() and sent
+// to all the registered Tracks.
+class CONTENT_EXPORT HtmlAudioElementCapturerSource final
+    : NON_EXPORTED_BASE(public MediaStreamAudioSource) {
+ public:
+  static HtmlAudioElementCapturerSource*
+  CreateFromWebMediaPlayerImpl(blink::WebMediaPlayer* player);
+
+  explicit HtmlAudioElementCapturerSource(
+      const base::WeakPtr<media::WebAudioSourceProviderImpl>& audio_source);
+  ~HtmlAudioElementCapturerSource() override;
+
+ private:
+  // MediaStreamAudioSource implementation.
+  bool EnsureSourceIsStarted() final;
+  void EnsureSourceIsStopped() final;
+
+  // To act as an WebAudioSourceProviderImpl::CopyAudioCB.
+  void OnAudioBus(std::unique_ptr<media::AudioBus> audio_bus,
+                  uint32_t delay_milliseconds,
+                  int sample_rate);
+
+  base::WeakPtr<media::WebAudioSourceProviderImpl> audio_source_;
+
+  bool is_started_;
+  int last_sample_rate_;
+  int last_num_channels_;
+  int last_bus_frames_;
+
+  base::ThreadChecker thread_checker_;
+
+  DISALLOW_COPY_AND_ASSIGN(HtmlAudioElementCapturerSource);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_MEDIA_HTML_AUDIO_ELEMENT_CAPTURER_SOURCE_H_