Added volume adjust sound behind the flag.

media/audio/sounds/audio_stream_handler.cc

Index: media/audio/sounds/audio_stream_handler.cc
diff --git a/media/audio/sounds/audio_stream_handler.cc b/media/audio/sounds/audio_stream_handler.cc
index 49709769f7c54fde19caabc05c1afc303cf1886d..f905484ceefdcd507a88953fa57ec03219c0f8f9 100644
--- a/media/audio/sounds/audio_stream_handler.cc
+++ b/media/audio/sounds/audio_stream_handler.cc
@@ -8,6 +8,7 @@
 
 #include "base/logging.h"
 #include "base/single_thread_task_runner.h"
+#include "base/synchronization/lock.h"
 #include "media/audio/audio_manager.h"
 #include "media/audio/audio_manager_base.h"
 #include "media/base/channel_layout.h"
@@ -30,12 +31,11 @@ AudioOutputStream::AudioSourceCallback* g_audio_source_for_testing = NULL;
 class AudioStreamHandler::AudioStreamContainer
     : public AudioOutputStream::AudioSourceCallback {
  public:
-  AudioStreamContainer(const WavAudioHandler& wav_audio,
-                       const AudioParameters& params)
+  AudioStreamContainer(const WavAudioHandler& wav_audio)
       : stream_(NULL),
         wav_audio_(wav_audio),
-        params_(params),
-        cursor_(0) {
+        cursor_(0),
+        can_start_(true) {
   }
 
   virtual ~AudioStreamContainer() {
@@ -46,20 +46,25 @@ class AudioStreamHandler::AudioStreamContainer
     DCHECK(AudioManager::Get()->GetTaskRunner()->BelongsToCurrentThread());
 
     if (!stream_) {
-      stream_ = AudioManager::Get()->MakeAudioOutputStreamProxy(params_,
-                                                                std::string(),
-                                                                std::string());
+      const AudioParameters& p = wav_audio_.params();
+      const AudioParameters params(AudioParameters::AUDIO_PCM_LOW_LATENCY,
+                                   p.channel_layout(),
+                                   p.sample_rate(),
+                                   p.bits_per_sample(),
+                                   kDefaultFrameCount);
+      stream_ = AudioManager::Get()->MakeAudioOutputStreamProxy(
+          params, std::string(), std::string());
       if (!stream_ || !stream_->Open()) {
         LOG(ERROR) << "Failed to open an output stream.";
         return;
       }
       stream_->SetVolume(kOutputVolumePercent);
-    } else {
-      // TODO (ygorshenin@): implement smart stream rewind.
-      stream_->Stop();
+    } else if (!CanStart()) {

[DaleCurtis, 2014/01/09 19:58:26]

You can simplify this by tracking "started_" instead of "can_start_" and using a
base::CancelableClosure().  Doing so allows you to remove the extra lock and
avoid the explosion of Get/Set/Can methods.  Replace this else with:

<acquire lock_>
stop_callback_.Reset(base::Bind(
    &AudioStreamContainer::StopStream, base::Unretained(this)));
if (started_ && wav_audio_.AtEnd(cursor_)) {
  cursor_ = 0;
  return;
}
started_ = true;

Down below inside OnMoreData() change the PostTask() to a PostDelayedTask() with
a timeout of whatever you want for your keep alive duration (XXX):

<acquire lock_>
AudioManager::Get()->GetTaskRunner()->PostDelayedTask(
    FROM_HERE, stop_callback_, base::TimeDelta::FromSeconds(XXX));

Inside StopStream() just add a "started_ = false";

[ygorshenin1, 2014/01/13 10:00:55]

Done.

[ygorshenin1, 2014/01/13 10:00:55]

Done.

+      return;
     }
 
-    cursor_ = 0;
+    SetCursor(0);
+    SetCanStart(false);
     if (g_audio_source_for_testing)
       stream_->Start(g_audio_source_for_testing);
     else
@@ -71,14 +76,10 @@ class AudioStreamHandler::AudioStreamContainer
 
   void Stop() {
     DCHECK(AudioManager::Get()->GetTaskRunner()->BelongsToCurrentThread());
-    if (!stream_)
-      return;
-    stream_->Stop();
-    stream_->Close();
+    StopStream();
+    if (stream_)
+      stream_->Close();
     stream_ = NULL;
-
-    if (g_observer_for_testing)
-      g_observer_for_testing->OnStop(cursor_);
   }
 
  private:
@@ -87,14 +88,16 @@ class AudioStreamHandler::AudioStreamContainer
   virtual int OnMoreData(AudioBus* dest,
                          AudioBuffersState /* state */) OVERRIDE {
     size_t bytes_written = 0;
-    if (wav_audio_.AtEnd(cursor_) ||
-        !wav_audio_.CopyTo(dest, cursor_, &bytes_written)) {
+    size_t cursor = GetCursor();
+    if (wav_audio_.AtEnd(cursor) ||
+        !wav_audio_.CopyTo(dest, cursor, &bytes_written)) {
       AudioManager::Get()->GetTaskRunner()->PostTask(
           FROM_HERE,
-          base::Bind(&AudioStreamContainer::Stop, base::Unretained(this)));
+          base::Bind(&AudioStreamContainer::StopStream,
+                     base::Unretained(this)));
       return 0;
     }
-    cursor_ += bytes_written;
+    SetCursor(cursor + bytes_written);
 
     return dest->frames();
   }
@@ -109,13 +112,44 @@ class AudioStreamHandler::AudioStreamContainer
     LOG(ERROR) << "Error during system sound reproduction.";
   }
 
+  void StopStream() {
+    if (stream_)
+      stream_->Stop();
+    if (g_observer_for_testing)
+      g_observer_for_testing->OnStop(GetCursor());
+    SetCanStart(true);
+  }
+
+  size_t GetCursor() {
+    base::AutoLock al(cursor_lock_);
+    return cursor_;
+  }
+
+  void SetCursor(size_t cursor) {
+    base::AutoLock al(cursor_lock_);
+    cursor_ = cursor;
+  }
+
+  bool CanStart() {
+    base::AutoLock al(can_start_lock_);
+    return can_start_;
+  }
+
+  void SetCanStart(bool can_start) {
+    base::AutoLock al(can_start_lock_);
+    can_start_ = can_start;
+  }
+
   AudioOutputStream* stream_;
 
   const WavAudioHandler wav_audio_;
-  const AudioParameters params_;
 
+  base::Lock cursor_lock_;
   size_t cursor_;
 
+  base::Lock can_start_lock_;
+  bool can_start_;
+
   DISALLOW_COPY_AND_ASSIGN(AudioStreamContainer);
 };
 
@@ -127,16 +161,11 @@ AudioStreamHandler::AudioStreamHandler(const base::StringPiece& wav_data)
     LOG(ERROR) << "Can't get access to audio manager.";
     return;
   }
-  AudioParameters params(AudioParameters::AUDIO_PCM_LOW_LATENCY,
-                         GuessChannelLayout(wav_audio_.num_channels()),
-                         wav_audio_.sample_rate(),
-                         wav_audio_.bits_per_sample(),
-                         kDefaultFrameCount);
-  if (!params.IsValid()) {
+  if (!wav_audio_.params().IsValid()) {
     LOG(ERROR) << "Audio params are invalid.";
     return;
   }
-  stream_.reset(new AudioStreamContainer(wav_audio_, params));
+  stream_.reset(new AudioStreamContainer(wav_audio_));
   initialized_ = true;
 }