Break out WebAudio suspension code into new class. Add tests.

media/base/silent_sink_suspender.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 MEDIA_BASE_SILENT_SINK_SUSPENDER_H_
+#define MEDIA_BASE_SILENT_SINK_SUSPENDER_H_
+
+#include <stdint.h>
+
+#include <deque>
+
+#include "base/cancelable_callback.h"
+#include "base/compiler_specific.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/synchronization/lock.h"
+#include "base/time/time.h"
+#include "media/audio/fake_audio_worker.h"
+#include "media/base/audio_parameters.h"
+#include "media/base/audio_renderer_sink.h"
+#include "media/base/media_export.h"
+
+namespace base {
+class SingleThreadTaskRunner;
+}
+
+namespace media {
+
+// Helper class for suspending AudioRenderSink instances after silence has been
+// detected for some time. When this is detected, the provided |sink_| is paused
+// and a fake sink is injected to black hole the silent audio data and avoid
+// physical hardware usage.
+class MEDIA_EXPORT SilentSinkSuspender
+    : NON_EXPORTED_BASE(public AudioRendererSink::RenderCallback) {
+ public:
+  // |callback| is the true producer of audio data, |params| are the parameters
+  // used to initialize |sink|, |sink| is the sink to monitor for idle, and
+  // |worker| is the task runner to run the fake Render() callbacks on. The
+  // amount of silence to allow before suspension is |silence_timeout|.
+  SilentSinkSuspender(
+      AudioRendererSink::RenderCallback* callback,
+      base::TimeDelta silence_timeout,
+      const AudioParameters& params,
+      const scoped_refptr<AudioRendererSink>& sink,
+      const scoped_refptr<base::SingleThreadTaskRunner>& worker);
+  ~SilentSinkSuspender() override;
+
+  // AudioRendererSink::RenderCallback implementation.
+  int Render(AudioBus* dest,
+             uint32_t frames_delayed,
+             uint32_t frames_skipped) override;
+  void OnRenderError() override;
+
+  bool is_using_fake_sink_for_testing() const { return is_using_fake_sink_; }
+
+ private:
+  // If |use_fake_sink| is true, pauses |sink_| and plays |fake_sink_|; if
+  // false, pauses |fake_sink_| and plays |sink_|.
+  void TransitionSinks(bool use_fake_sink);
+
+  // Actual RenderCallback providing audio data to the output device.
+  AudioRendererSink::RenderCallback* const callback_;
+
+  // Parameters used to construct |sink_|.
+  const AudioParameters params_;
+
+  // Sink monitored for silent output.
+  scoped_refptr<AudioRendererSink> sink_;
+
+  // Task runner this class is constructed on. Used to run TransitionSinks().
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+
+  // Time when the silence starts.
+  base::TimeTicks first_silence_time_;
+
+  // Amount of time that can elapse before replacing |sink_| with |fake_sink_|.
+  const base::TimeDelta silence_timeout_;
+
+  // A fake audio sink object that consumes data when long period of silence
+  // audio is detected. This object lives on |task_runner_| and will run
+  // callbacks on RenderThreadImpl::GetMediaThreadTaskRunner().
+  FakeAudioWorker fake_sink_;
+
+  // AudioRendererSink::Pause() is not synchronous, so we need a lock to ensure
+  // we don't have concurrent access to Render().
+  base::Lock transition_lock_;
+
+  // Whether audio output is directed to |fake_sink_|. Must only be used when
+  // |transition_lock_| is held or both sinks are stopped.
+  bool is_using_fake_sink_ = false;
+
+  // Whether we're in the middle of a transition to or from |fake_sink_|. Must
+  // only be used when |transition_lock_| is held or both sinks are stopped.
+  bool is_transition_pending_ = false;
+
+  // Buffers accumulated during the transition from |fake_sink_| to |sink_|.
+  std::deque<std::unique_ptr<AudioBus>> buffers_after_silence_;
+
+  // A cancelable task that is posted to switch to or from the |fake_sink_|
+  // after a period of silence or first non-silent audio respective. We do this
+  // on Android to save battery consumption.
+  base::CancelableCallback<void(bool)> sink_transition_callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(SilentSinkSuspender);
+};
+
+}  // namespace content
+
+#endif  // MEDIA_BASE_SILENT_SINK_SUSPENDER_H_