Tab Audio Mirroring/Capture: Browser-side connect/disconnect functionality:

1. Added new AudioMirroringManager to dynamically match/route "divertable" audio streams with mirroring destinations.
2. Modified AudioOutputController to provide "divert audio data" functionality.
3. Modified AudioRendererHost to notify AudioMirroringManager of all audio streams.

The intention is, in a later change, to introduce a "WebContentsAudioInputStream" which will implement the AudioMirroringManager::MirroringDestination interface introduced in this change.  WCAIS will represent the lifetime of a tab audio mirroring session, calling AudioMirroringManager::Start/StopMirroring() as appropriate.

Testing:

1. Rewrote most of unit testing for AudioOutputController, addressing bug 112500.  Also added testing for the new Divert functionality.
2. Added extensive unit testing for the new Start/StopMirroring functionality in AudioMirroringManager.
3. Minor testing clean-ups/additions elsewhere.

BUG=153392,112500
TEST=Run media_unittests and content_unittests.


Review URL: https://chromiumcodereview.appspot.com/11413078

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@176295 0039d316-1c4b-4281-b951-d872f2087c98

5 files changed, 404 insertions, 212 deletions

diff --git a/media/audio/audio_output_controller.cc b/media/audio/audio_output_controller.cc
index a9dd2c8..ffeb639 100644
--- a/media/audio/audio_output_controller.cc
+++ b/media/audio/audio_output_controller.cc
@@ -29,14 +29,15 @@ AudioOutputController::AudioOutputController(AudioManager* audio_manager,
                                              const AudioParameters& params,
                                              SyncReader* sync_reader)
     : audio_manager_(audio_manager),
+      params_(params),
       handler_(handler),
       stream_(NULL),
+      diverting_to_stream_(NULL),
       volume_(1.0),
       state_(kEmpty),
       sync_reader_(sync_reader),
       message_loop_(audio_manager->GetMessageLoop()),
       number_polling_attempts_left_(0),
-      params_(params),
       ALLOW_THIS_IN_INITIALIZER_LIST(weak_this_(this)) {
 }
 
@@ -70,13 +71,10 @@ scoped_refptr<AudioOutputController> AudioOutputController::Create(
   if (!params.IsValid() || !audio_manager)
     return NULL;
 
-  // Starts the audio controller thread.
   scoped_refptr<AudioOutputController> controller(new AudioOutputController(
       audio_manager, event_handler, params, sync_reader));
-
   controller->message_loop_->PostTask(FROM_HERE, base::Bind(
       &AudioOutputController::DoCreate, controller));
-
   return controller;
 }
 
@@ -121,7 +119,8 @@ void AudioOutputController::DoCreate() {
 
   DoStopCloseAndClearStream(NULL);  // Calls RemoveOutputDeviceChangeListener().
 
-  stream_ = audio_manager_->MakeAudioOutputStreamProxy(params_);
+  stream_ = diverting_to_stream_ ? diverting_to_stream_ :
+      audio_manager_->MakeAudioOutputStreamProxy(params_);
   if (!stream_) {
     state_ = kError;
 
@@ -139,9 +138,10 @@ void AudioOutputController::DoCreate() {
     return;
   }
 
-  // Everything started okay, so register for state change callbacks if we have
-  // not already done so.
-  audio_manager_->AddOutputDeviceChangeListener(this);
+  // Everything started okay, so re-register for state change callbacks if
+  // stream_ was created via AudioManager.
+  if (stream_ != diverting_to_stream_)
+    audio_manager_->AddOutputDeviceChangeListener(this);
 
   // We have successfully opened the stream. Set the initial volume.
   stream_->SetVolume(volume_);
@@ -349,10 +349,15 @@ void AudioOutputController::DoStopCloseAndClearStream(WaitableEvent* done) {
 
   // Allow calling unconditionally and bail if we don't have a stream_ to close.
   if (stream_) {
-    audio_manager_->RemoveOutputDeviceChangeListener(this);
+    // De-register from state change callbacks if stream_ was created via
+    // AudioManager.
+    if (stream_ != diverting_to_stream_)
+      audio_manager_->RemoveOutputDeviceChangeListener(this);
 
     stream_->Stop();
     stream_->Close();
+    if (stream_ == diverting_to_stream_)
+      diverting_to_stream_ = NULL;
     stream_ = NULL;
 
     weak_this_.InvalidateWeakPtrs();
@@ -366,9 +371,6 @@ void AudioOutputController::DoStopCloseAndClearStream(WaitableEvent* done) {
 void AudioOutputController::OnDeviceChange() {
   DCHECK(message_loop_->BelongsToCurrentThread());
 
-  // We should always have a stream by this point.
-  CHECK(stream_);
-
   // Recreate the stream (DoCreate() will first shut down an existing stream).
   // Exit if we ran into an error.
   const State original_state = state_;
@@ -393,4 +395,46 @@ void AudioOutputController::OnDeviceChange() {
   }
 }
 
+const AudioParameters& AudioOutputController::GetAudioParameters() {
+  return params_;
+}
+
+void AudioOutputController::StartDiverting(AudioOutputStream* to_stream) {
+  message_loop_->PostTask(
+      FROM_HERE,
+      base::Bind(&AudioOutputController::DoStartDiverting, this, to_stream));
+}
+
+void AudioOutputController::StopDiverting() {
+  message_loop_->PostTask(
+      FROM_HERE, base::Bind(&AudioOutputController::DoStopDiverting, this));
+}
+
+void AudioOutputController::DoStartDiverting(AudioOutputStream* to_stream) {
+  DCHECK(message_loop_->BelongsToCurrentThread());
+
+  if (state_ == kClosed)
+    return;
+
+  DCHECK(!diverting_to_stream_);
+  diverting_to_stream_ = to_stream;
+  // Note: OnDeviceChange() will engage the "re-create" process, which will
+  // detect and use the alternate AudioOutputStream rather than create a new one
+  // via AudioManager.
+  OnDeviceChange();
+}
+
+void AudioOutputController::DoStopDiverting() {
+  DCHECK(message_loop_->BelongsToCurrentThread());
+
+  if (state_ == kClosed)
+    return;
+
+  // Note: OnDeviceChange() will cause the existing stream (the consumer of the
+  // diverted audio data) to be closed, and diverting_to_stream_ will be set
+  // back to NULL.
+  OnDeviceChange();
+  DCHECK(!diverting_to_stream_);
+}
+
 }  // namespace media
diff --git a/media/audio/audio_output_controller.h b/media/audio/audio_output_controller.h
index 61718a3..21f8efe 100644
--- a/media/audio/audio_output_controller.h
+++ b/media/audio/audio_output_controller.h
@@ -12,6 +12,7 @@
 #include "media/audio/audio_buffers_state.h"
 #include "media/audio/audio_io.h"
 #include "media/audio/audio_manager.h"
+#include "media/audio/audio_source_diverter.h"
 #include "media/audio/simple_sources.h"
 #include "media/base/media_export.h"
 
@@ -66,6 +67,7 @@ namespace media {
 class MEDIA_EXPORT AudioOutputController
     : public base::RefCountedThreadSafe<AudioOutputController>,
       public AudioOutputStream::AudioSourceCallback,
+      public AudioSourceDiverter,
       NON_EXPORTED_BASE(public AudioManager::AudioDeviceListener)  {
  public:
   // An event handler that receives events from the AudioOutputController. The
@@ -154,8 +156,13 @@ class MEDIA_EXPORT AudioOutputController
   // to being called.
   virtual void OnDeviceChange() OVERRIDE;
 
+  // AudioSourceDiverter implementation.
+  virtual const AudioParameters& GetAudioParameters() OVERRIDE;
+  virtual void StartDiverting(AudioOutputStream* to_stream) OVERRIDE;
+  virtual void StopDiverting() OVERRIDE;
+
  protected:
-    // Internal state of the source.
+  // Internal state of the source.
   enum State {
     kEmpty,
     kCreated,
@@ -188,6 +195,8 @@ class MEDIA_EXPORT AudioOutputController
   void DoClose();
   void DoSetVolume(double volume);
   void DoReportError(int code);
+  void DoStartDiverting(AudioOutputStream* to_stream);
+  void DoStopDiverting();
 
   // Helper method that starts physical stream.
   void StartStream();
@@ -197,6 +206,7 @@ class MEDIA_EXPORT AudioOutputController
   void DoStopCloseAndClearStream(base::WaitableEvent *done);
 
   AudioManager* const audio_manager_;
+  const AudioParameters params_;
 
   // |handler_| may be called only if |state_| is not kClosed.
   EventHandler* handler_;
@@ -205,6 +215,9 @@ class MEDIA_EXPORT AudioOutputController
   // changed.  See comment for weak_this_.
   AudioOutputStream* stream_;
 
+  // When non-NULL, audio is being diverted to this stream.
+  AudioOutputStream* diverting_to_stream_;
+
   // The current volume of the audio stream.
   double volume_;
 
@@ -227,8 +240,6 @@ class MEDIA_EXPORT AudioOutputController
   // Number of times left.
   int number_polling_attempts_left_;
 
-  AudioParameters params_;
-
   // Used to auto-cancel the delayed tasks that are created to poll for data
   // (when starting-up a stream).
   base::WeakPtrFactory<AudioOutputController> weak_this_;
diff --git a/media/audio/audio_output_controller_unittest.cc b/media/audio/audio_output_controller_unittest.cc
index fe29ce5..ff37b5a 100644
--- a/media/audio/audio_output_controller_unittest.cc
+++ b/media/audio/audio_output_controller_unittest.cc
@@ -2,23 +2,24 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include "base/basictypes.h"
 #include "base/bind.h"
 #include "base/environment.h"
-#include "base/basictypes.h"
 #include "base/logging.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
 #include "base/message_loop.h"
 #include "base/synchronization/waitable_event.h"
 #include "media/audio/audio_output_controller.h"
+#include "media/audio/audio_parameters.h"
+#include "media/base/audio_bus.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
-// TODO(vrk): These tests need to be rewritten! (crbug.com/112500)
-
 using ::testing::_;
 using ::testing::AtLeast;
 using ::testing::DoAll;
-using ::testing::Exactly;
-using ::testing::InvokeWithoutArgs;
+using ::testing::Invoke;
 using ::testing::NotNull;
 using ::testing::Return;
 
@@ -27,9 +28,10 @@ namespace media {
 static const int kSampleRate = AudioParameters::kAudioCDSampleRate;
 static const int kBitsPerSample = 16;
 static const ChannelLayout kChannelLayout = CHANNEL_LAYOUT_STEREO;
-static const int kSamplesPerPacket = kSampleRate / 10;
+static const int kSamplesPerPacket = kSampleRate / 100;
 static const int kHardwareBufferSize = kSamplesPerPacket *
     ChannelLayoutToChannelCount(kChannelLayout) * kBitsPerSample / 8;
+static const double kTestVolume = 0.25;
 
 class MockAudioOutputControllerEventHandler
     : public AudioOutputController::EventHandler {
@@ -60,227 +62,321 @@ class MockAudioOutputControllerSyncReader
   DISALLOW_COPY_AND_ASSIGN(MockAudioOutputControllerSyncReader);
 };
 
+class MockAudioOutputStream : public AudioOutputStream {
+ public:
+  MOCK_METHOD0(Open, bool());
+  MOCK_METHOD1(Start, void(AudioSourceCallback* callback));
+  MOCK_METHOD0(Stop, void());
+  MOCK_METHOD1(SetVolume, void(double volume));
+  MOCK_METHOD1(GetVolume, void(double* volume));
+  MOCK_METHOD0(Close, void());
+
+  // Set/get the callback passed to Start().
+  AudioSourceCallback* callback() const { return callback_; }
+  void SetCallback(AudioSourceCallback* asc) { callback_ = asc; }
+
+ private:
+  AudioSourceCallback* callback_;
+};
+
 ACTION_P(SignalEvent, event) {
   event->Signal();
 }
 
-// Custom action to clear a memory buffer.
-ACTION(ClearBuffer) {
+static const float kBufferNonZeroData = 1.0f;
+ACTION(PopulateBuffer) {
   arg1->Zero();
-}
-
-// Closes AudioOutputController synchronously.
-static void CloseAudioController(AudioOutputController* controller) {
-  controller->Close(MessageLoop::QuitClosure());
-  MessageLoop::current()->Run();
+  // Note: To confirm the buffer will be populated in these tests, it's
+  // sufficient that only the first float in channel 0 is set to the value.
+  arg1->channel(0)[0] = kBufferNonZeroData;
 }
 
 class AudioOutputControllerTest : public testing::Test {
  public:
-  AudioOutputControllerTest() {}
-  virtual ~AudioOutputControllerTest() {}
+  AudioOutputControllerTest()
+      : audio_manager_(AudioManager::Create()),
+        create_event_(false, false),
+        play_event_(false, false),
+        read_event_(false, false),
+        pause_event_(false, false) {
+  }
+
+  virtual ~AudioOutputControllerTest() {
+  }
 
  protected:
-  MessageLoopForIO message_loop_;
+  void Create(int samples_per_packet) {
+    EXPECT_FALSE(create_event_.IsSignaled());
+    EXPECT_FALSE(play_event_.IsSignaled());
+    EXPECT_FALSE(read_event_.IsSignaled());
+    EXPECT_FALSE(pause_event_.IsSignaled());
+
+    params_ = AudioParameters(
+        AudioParameters::AUDIO_FAKE, kChannelLayout,
+        kSampleRate, kBitsPerSample, samples_per_packet);
+
+    if (params_.IsValid()) {
+      EXPECT_CALL(mock_event_handler_, OnCreated(NotNull()))
+          .WillOnce(SignalEvent(&create_event_));
+    }
+
+    controller_ = AudioOutputController::Create(
+        audio_manager_.get(), &mock_event_handler_, params_,
+        &mock_sync_reader_);
+    if (controller_)
+      controller_->SetVolume(kTestVolume);
+
+    EXPECT_EQ(params_.IsValid(), controller_ != NULL);
+  }
+
+  void Play() {
+    // Expect the event handler to receive one OnPlaying() call.
+    EXPECT_CALL(mock_event_handler_, OnPlaying(NotNull()))
+        .WillOnce(SignalEvent(&play_event_));
+
+    // During playback, the mock pretends to provide audio data rendered and
+    // sent from the render process.
+    EXPECT_CALL(mock_sync_reader_, UpdatePendingBytes(_))
+        .Times(AtLeast(2));
+    EXPECT_CALL(mock_sync_reader_, Read(_, _))
+        .WillRepeatedly(DoAll(PopulateBuffer(),
+                              SignalEvent(&read_event_),
+                              Return(params_.frames_per_buffer())));
+    EXPECT_CALL(mock_sync_reader_, DataReady())
+        .WillRepeatedly(Return(true));
+
+    controller_->Play();
+  }
+
+  void Pause() {
+    // Expect the event handler to receive one OnPaused() call.
+    EXPECT_CALL(mock_event_handler_, OnPaused(NotNull()))
+        .WillOnce(SignalEvent(&pause_event_));
+
+    controller_->Pause();
+  }
+
+  void ChangeDevice() {
+    // Expect the event handler to receive one OnPaying() call and no OnPaused()
+    // call.
+    EXPECT_CALL(mock_event_handler_, OnPlaying(NotNull()))
+        .WillOnce(SignalEvent(&play_event_));
+    EXPECT_CALL(mock_event_handler_, OnPaused(NotNull()))
+        .Times(0);
+
+    // Simulate a device change event to AudioOutputController from the
+    // AudioManager.
+    audio_manager_->GetMessageLoop()->PostTask(
+        FROM_HERE,
+        base::Bind(&AudioOutputController::OnDeviceChange, controller_));
+  }
+
+  void Divert(bool was_playing, bool will_be_playing) {
+    if (was_playing) {
+      // Expect the handler to receive one OnPlaying() call as a result of the
+      // stream switching.
+      EXPECT_CALL(mock_event_handler_, OnPlaying(NotNull()))
+          .WillOnce(SignalEvent(&play_event_));
+    }
+
+    EXPECT_CALL(mock_stream_, Open())
+        .WillOnce(Return(true));
+    EXPECT_CALL(mock_stream_, SetVolume(kTestVolume));
+    if (will_be_playing) {
+      EXPECT_CALL(mock_stream_, Start(NotNull()))
+          .Times(AtLeast(1))
+          .WillRepeatedly(
+              Invoke(&mock_stream_, &MockAudioOutputStream::SetCallback));
+    }
+    // Always expect a Stop() call--even without a Start() call--since
+    // AudioOutputController likes to play it safe and Stop() before any
+    // Close().
+    EXPECT_CALL(mock_stream_, Stop())
+        .Times(AtLeast(1));
+
+    controller_->StartDiverting(&mock_stream_);
+  }
+
+  void ReadDivertedAudioData() {
+    scoped_ptr<AudioBus> dest = AudioBus::Create(params_);
+    ASSERT_TRUE(!!mock_stream_.callback());
+    const int frames_read =
+        mock_stream_.callback()->OnMoreData(dest.get(), AudioBuffersState());
+    EXPECT_LT(0, frames_read);
+    EXPECT_EQ(kBufferNonZeroData, dest->channel(0)[0]);
+  }
+
+  void Revert(bool was_playing) {
+    if (was_playing) {
+      // Expect the handler to receive one OnPlaying() call as a result of the
+      // stream switching back.
+      EXPECT_CALL(mock_event_handler_, OnPlaying(NotNull()))
+          .WillOnce(SignalEvent(&play_event_));
+    }
+
+    EXPECT_CALL(mock_stream_, Close());
+
+    controller_->StopDiverting();
+  }
+
+  void Close() {
+    EXPECT_CALL(mock_sync_reader_, Close());
+
+    controller_->Close(MessageLoop::QuitClosure());
+    MessageLoop::current()->Run();
+  }
+
+  // These help make test sequences more readable.
+  void DivertNeverPlaying() { Divert(false, false); }
+  void DivertWillEventuallyBePlaying() { Divert(false, true); }
+  void DivertWhilePlaying() { Divert(true, true); }
+  void RevertWasNotPlaying() { Revert(false); }
+  void RevertWhilePlaying() { Revert(true); }
+
+  // These synchronize the main thread with key events taking place on other
+  // threads.
+  void WaitForCreate() { create_event_.Wait(); }
+  void WaitForPlay() { play_event_.Wait(); }
+  void WaitForReads() {
+    // Note: Arbitrarily chosen, but more iterations causes tests to take
+    // significantly more time.
+    static const int kNumIterations = 3;
+    for (int i = 0; i < kNumIterations; ++i) {
+      read_event_.Wait();
+    }
+  }
+  void WaitForPause() { pause_event_.Wait(); }
 
  private:
+  MessageLoopForIO message_loop_;
+  scoped_ptr<AudioManager> audio_manager_;
+  MockAudioOutputControllerEventHandler mock_event_handler_;
+  MockAudioOutputControllerSyncReader mock_sync_reader_;
+  MockAudioOutputStream mock_stream_;
+  base::WaitableEvent create_event_;
+  base::WaitableEvent play_event_;
+  base::WaitableEvent read_event_;
+  base::WaitableEvent pause_event_;
+  AudioParameters params_;
+  scoped_refptr<AudioOutputController> controller_;
+
   DISALLOW_COPY_AND_ASSIGN(AudioOutputControllerTest);
 };
 
 TEST_F(AudioOutputControllerTest, CreateAndClose) {
-  scoped_ptr<AudioManager> audio_manager(AudioManager::Create());
-  if (!audio_manager->HasAudioOutputDevices())
-    return;
+  Create(kSamplesPerPacket);
+  Close();
+}
 
-  MockAudioOutputControllerEventHandler event_handler;
+TEST_F(AudioOutputControllerTest, HardwareBufferTooLarge) {
+  Create(kSamplesPerPacket * 1000);
+}
 
-  EXPECT_CALL(event_handler, OnCreated(NotNull()))
-      .Times(1);
+TEST_F(AudioOutputControllerTest, PlayAndClose) {
+  Create(kSamplesPerPacket);
+  WaitForCreate();
+  Play();
+  WaitForPlay();
+  WaitForReads();
+  Close();
+}
 
-  MockAudioOutputControllerSyncReader sync_reader;
-  EXPECT_CALL(sync_reader, Close());
+TEST_F(AudioOutputControllerTest, PlayPauseClose) {
+  Create(kSamplesPerPacket);
+  WaitForCreate();
+  Play();
+  WaitForPlay();
+  WaitForReads();
+  Pause();
+  WaitForPause();
+  Close();
+}
 
-  AudioParameters params(AudioParameters::AUDIO_PCM_LINEAR, kChannelLayout,
-                         kSampleRate, kBitsPerSample, kSamplesPerPacket);
-  scoped_refptr<AudioOutputController> controller =
-      AudioOutputController::Create(
-          audio_manager.get(), &event_handler, params, &sync_reader);
-  ASSERT_TRUE(controller.get());
+TEST_F(AudioOutputControllerTest, PlayPausePlayClose) {
+  Create(kSamplesPerPacket);
+  WaitForCreate();
+  Play();
+  WaitForPlay();
+  WaitForReads();
+  Pause();
+  WaitForPause();
+  Play();
+  WaitForPlay();
+  Close();
+}
 
-  // Close the controller immediately.
-  CloseAudioController(controller);
+TEST_F(AudioOutputControllerTest, PlayDeviceChangeClose) {
+  Create(kSamplesPerPacket);
+  WaitForCreate();
+  Play();
+  WaitForPlay();
+  WaitForReads();
+  ChangeDevice();
+  WaitForPlay();
+  WaitForReads();
+  Close();
 }
 
-TEST_F(AudioOutputControllerTest, PlayPauseClose) {
-  scoped_ptr<AudioManager> audio_manager(AudioManager::Create());
-  if (!audio_manager->HasAudioOutputDevices())
-    return;
-
-  MockAudioOutputControllerEventHandler event_handler;
-  base::WaitableEvent event(false, false);
-  base::WaitableEvent pause_event(false, false);
-
-  // If OnCreated is called then signal the event.
-  EXPECT_CALL(event_handler, OnCreated(NotNull()))
-      .WillOnce(InvokeWithoutArgs(&event, &base::WaitableEvent::Signal));
-
-  // OnPlaying() will be called only once.
-  EXPECT_CALL(event_handler, OnPlaying(NotNull()));
-
-  MockAudioOutputControllerSyncReader sync_reader;
-  EXPECT_CALL(sync_reader, UpdatePendingBytes(_))
-      .Times(AtLeast(2));
-  EXPECT_CALL(sync_reader, Read(_, _))
-      .WillRepeatedly(DoAll(ClearBuffer(), SignalEvent(&event),
-                            Return(4)));
-  EXPECT_CALL(sync_reader, DataReady())
-      .WillRepeatedly(Return(true));
-  EXPECT_CALL(event_handler, OnPaused(NotNull()))
-      .WillOnce(InvokeWithoutArgs(&pause_event, &base::WaitableEvent::Signal));
-  EXPECT_CALL(sync_reader, Close());
-
-  AudioParameters params(AudioParameters::AUDIO_PCM_LINEAR, kChannelLayout,
-                         kSampleRate, kBitsPerSample, kSamplesPerPacket);
-  scoped_refptr<AudioOutputController> controller =
-      AudioOutputController::Create(
-          audio_manager.get(), &event_handler, params, &sync_reader);
-  ASSERT_TRUE(controller.get());
-
-  // Wait for OnCreated() to be called.
-  event.Wait();
-
-  ASSERT_FALSE(pause_event.IsSignaled());
-  controller->Play();
-  controller->Pause();
-  pause_event.Wait();
-
-  // Now stop the controller.
-  CloseAudioController(controller);
+TEST_F(AudioOutputControllerTest, PlayDivertRevertClose) {
+  Create(kSamplesPerPacket);
+  WaitForCreate();
+  Play();
+  WaitForPlay();
+  WaitForReads();
+  DivertWhilePlaying();
+  WaitForPlay();
+  ReadDivertedAudioData();
+  RevertWhilePlaying();
+  WaitForPlay();
+  WaitForReads();
+  Close();
 }
 
-TEST_F(AudioOutputControllerTest, HardwareBufferTooLarge) {
-  scoped_ptr<AudioManager> audio_manager(AudioManager::Create());
-  if (!audio_manager->HasAudioOutputDevices())
-    return;
-
-  // Create an audio device with a very large hardware buffer size.
-  MockAudioOutputControllerEventHandler event_handler;
-
-  MockAudioOutputControllerSyncReader sync_reader;
-  AudioParameters params(AudioParameters::AUDIO_PCM_LINEAR, kChannelLayout,
-                         kSampleRate, kBitsPerSample,
-                         kSamplesPerPacket * 1000);
-  scoped_refptr<AudioOutputController> controller =
-      AudioOutputController::Create(
-          audio_manager.get(), &event_handler, params, &sync_reader);
-
-  // Use assert because we don't stop the device and assume we can't
-  // create one.
-  ASSERT_FALSE(controller);
+TEST_F(AudioOutputControllerTest, PlayDivertRevertDivertRevertClose) {
+  Create(kSamplesPerPacket);
+  WaitForCreate();
+  Play();
+  WaitForPlay();
+  WaitForReads();
+  DivertWhilePlaying();
+  WaitForPlay();
+  ReadDivertedAudioData();
+  RevertWhilePlaying();
+  WaitForPlay();
+  WaitForReads();
+  DivertWhilePlaying();
+  WaitForPlay();
+  ReadDivertedAudioData();
+  RevertWhilePlaying();
+  WaitForPlay();
+  WaitForReads();
+  Close();
 }
 
-TEST_F(AudioOutputControllerTest, PlayPausePlayClose) {
-  scoped_ptr<AudioManager> audio_manager(AudioManager::Create());
-  if (!audio_manager->HasAudioOutputDevices())
-    return;
-
-  MockAudioOutputControllerEventHandler event_handler;
-  base::WaitableEvent event(false, false);
-  EXPECT_CALL(event_handler, OnCreated(NotNull()))
-      .WillOnce(InvokeWithoutArgs(&event, &base::WaitableEvent::Signal));
-
-  // OnPlaying() will be called only once.
-  base::WaitableEvent play_event(false, false);
-  EXPECT_CALL(event_handler, OnPlaying(NotNull()))
-      .WillOnce(InvokeWithoutArgs(&play_event, &base::WaitableEvent::Signal));
-
-  // OnPaused() should never be called since the pause during kStarting is
-  // dropped when the second play comes in.
-  EXPECT_CALL(event_handler, OnPaused(NotNull()))
-      .Times(0);
-
-  MockAudioOutputControllerSyncReader sync_reader;
-  EXPECT_CALL(sync_reader, UpdatePendingBytes(_))
-      .Times(AtLeast(1));
-  EXPECT_CALL(sync_reader, Read(_, _))
-      .WillRepeatedly(DoAll(ClearBuffer(), SignalEvent(&event), Return(4)));
-  EXPECT_CALL(sync_reader, DataReady())
-      .WillRepeatedly(Return(true));
-  EXPECT_CALL(sync_reader, Close());
-
-  AudioParameters params(AudioParameters::AUDIO_PCM_LINEAR, kChannelLayout,
-                         kSampleRate, kBitsPerSample, kSamplesPerPacket);
-  scoped_refptr<AudioOutputController> controller =
-      AudioOutputController::Create(
-          audio_manager.get(), &event_handler, params, &sync_reader);
-  ASSERT_TRUE(controller.get());
-
-  // Wait for OnCreated() to be called.
-  event.Wait();
-
-  ASSERT_FALSE(play_event.IsSignaled());
-  controller->Play();
-  controller->Pause();
-  controller->Play();
-  play_event.Wait();
-
-  // Now stop the controller.
-  CloseAudioController(controller);
+TEST_F(AudioOutputControllerTest, DivertPlayPausePlayRevertClose) {
+  Create(kSamplesPerPacket);
+  WaitForCreate();
+  DivertWillEventuallyBePlaying();
+  Play();
+  WaitForPlay();
+  ReadDivertedAudioData();
+  Pause();
+  WaitForPause();
+  Play();
+  WaitForPlay();
+  ReadDivertedAudioData();
+  RevertWhilePlaying();
+  WaitForPlay();
+  WaitForReads();
+  Close();
 }
 
-// Ensure state change events are handled.
-TEST_F(AudioOutputControllerTest, PlayStateChangeClose) {
-  scoped_ptr<AudioManager> audio_manager(AudioManager::Create());
-  if (!audio_manager->HasAudioOutputDevices())
-    return;
-
-  MockAudioOutputControllerEventHandler event_handler;
-  base::WaitableEvent event(false, false);
-  EXPECT_CALL(event_handler, OnCreated(NotNull()))
-      .WillOnce(InvokeWithoutArgs(&event, &base::WaitableEvent::Signal));
-
-  // OnPlaying() will be called once normally and once after being recreated.
-  base::WaitableEvent play_event(false, false);
-  EXPECT_CALL(event_handler, OnPlaying(NotNull()))
-      .Times(2)
-      .WillRepeatedly(InvokeWithoutArgs(
-          &play_event, &base::WaitableEvent::Signal));
-
-  // OnPaused() should not be called during the state change event.
-  EXPECT_CALL(event_handler, OnPaused(NotNull()))
-      .Times(0);
-
-  MockAudioOutputControllerSyncReader sync_reader;
-  EXPECT_CALL(sync_reader, UpdatePendingBytes(_))
-      .Times(AtLeast(1));
-  EXPECT_CALL(sync_reader, Read(_, _))
-      .WillRepeatedly(DoAll(ClearBuffer(), SignalEvent(&event), Return(4)));
-  EXPECT_CALL(sync_reader, DataReady())
-      .WillRepeatedly(Return(true));
-  EXPECT_CALL(sync_reader, Close());
-
-  AudioParameters params(AudioParameters::AUDIO_PCM_LINEAR, kChannelLayout,
-                         kSampleRate, kBitsPerSample, kSamplesPerPacket);
-  scoped_refptr<AudioOutputController> controller =
-      AudioOutputController::Create(
-          audio_manager.get(), &event_handler, params, &sync_reader);
-  ASSERT_TRUE(controller.get());
-
-  // Wait for OnCreated() to be called.
-  event.Wait();
-
-  ASSERT_FALSE(play_event.IsSignaled());
-  controller->Play();
-  play_event.Wait();
-
-  // Force a state change and wait for the stream to come back to playing state.
-  play_event.Reset();
-  audio_manager->GetMessageLoop()->PostTask(FROM_HERE,
-      base::Bind(&AudioOutputController::OnDeviceChange, controller));
-  play_event.Wait();
-
-  // Now stop the controller.
-  CloseAudioController(controller);
+TEST_F(AudioOutputControllerTest, DivertRevertClose) {
+  Create(kSamplesPerPacket);
+  WaitForCreate();
+  DivertNeverPlaying();
+  RevertWasNotPlaying();
+  Close();
 }
 
 }  // namespace media
diff --git a/media/audio/audio_source_diverter.h b/media/audio/audio_source_diverter.h
new file mode 100644
index 0000000..787ddec
--- /dev/null
+++ b/media/audio/audio_source_diverter.h
@@ -0,0 +1,40 @@
+// Copyright (c) 2013 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_AUDIO_AUDIO_SOURCE_DIVERTER_H_
+#define MEDIA_AUDIO_AUDIO_SOURCE_DIVERTER_H_
+
+#include "media/base/media_export.h"
+
+// Audio sources may optionally implement AudioSourceDiverter to temporarily
+// divert audio data to an alternate AudioOutputStream.  This allows the audio
+// data to be plumbed to an alternate consumer; for example, a loopback
+// mechanism for audio mirroring.
+
+namespace media {
+
+class AudioOutputStream;
+class AudioParameters;
+
+class MEDIA_EXPORT AudioSourceDiverter {
+public:
+  // Returns the audio parameters of the divertable audio data.
+  virtual const AudioParameters& GetAudioParameters() = 0;
+
+  // Start providing audio data to the given |to_stream|, which is in an
+  // unopened state.  |to_stream| remains under the control of the
+  // AudioSourceDiverter.
+  virtual void StartDiverting(AudioOutputStream* to_stream) = 0;
+
+  // Stops diverting audio data to the stream.  The AudioSourceDiverter is
+  // responsible for making sure the stream is closed, perhaps asynchronously.
+  virtual void StopDiverting() = 0;
+
+protected:
+  virtual ~AudioSourceDiverter() {}
+};
+
+}  // namespace media
+
+#endif  // MEDIA_AUDIO_AUDIO_SOURCE_DIVERTER_H_
diff --git a/media/media.gyp b/media/media.gyp
index 05b35cc..feb1cc5 100644
--- a/media/media.gyp
+++ b/media/media.gyp
@@ -83,6 +83,7 @@
         'audio/audio_output_proxy.h',
         'audio/audio_output_resampler.cc',
         'audio/audio_output_resampler.h',
+        'audio/audio_source_diverter.h',
         'audio/audio_util.cc',
         'audio/audio_util.h',
         'audio/cross_process_notification.cc',