Remove Mac input audio restart mechanism and reduce time until startup success check.

media/audio/mac/audio_low_latency_input_mac.h

Index: media/audio/mac/audio_low_latency_input_mac.h
diff --git a/media/audio/mac/audio_low_latency_input_mac.h b/media/audio/mac/audio_low_latency_input_mac.h
index b30b604193b55cba4101cf23f6428cf31b82a60b..df2f7a7315487a6f21a6ed6fa70e503dd947b9d3 100644
--- a/media/audio/mac/audio_low_latency_input_mac.h
+++ b/media/audio/mac/audio_low_latency_input_mac.h
@@ -130,9 +130,6 @@ class MEDIA_EXPORT AUAudioInputStream
   // (CrBrowserMain) which is the same thread as this instance is created on.
   void DevicePropertyChangedOnMainThread(const std::vector<UInt32>& properties);
 
-  // Updates |last_callback_time_| on the main browser thread.
-  void UpdateDataCallbackTimeOnMainThread(base::TimeTicks now_tick);
-
   // Registers OnDevicePropertyChanged() to receive notifications when device
   // properties changes.
   void RegisterDeviceChangeListener();
@@ -162,22 +159,12 @@ class MEDIA_EXPORT AUAudioInputStream
 
   // Checks if a stream was started successfully and the audio unit also starts
   // to call InputProc() as it should. This method is called once when a timer
-  // expires 5 seconds after calling Start().
+  // expires some time after calling Start().
   void CheckInputStartupSuccess();
 
-  // Checks (periodically) if a stream is alive by comparing the current time
-  // with the last timestamp stored in a data callback. Calls RestartAudio()
-  // when a restart is required.
-  void CheckIfInputStreamIsAlive();
-
   // Uninitializes the audio unit if needed.
   void CloseAudioUnit();
 
-  // Called by CheckIfInputStreamIsAlive() on the main thread when an audio
-  // restarts is required. Restarts the existing audio stream reusing the
-  // current audio parameters.
-  void RestartAudio();
-
   // Adds extra UMA stats when it has been detected that startup failed.
   void AddHistogramsForFailedStartup();
 
@@ -252,8 +239,14 @@ class MEDIA_EXPORT AUAudioInputStream
   // if length of error sequence is above a certain limit.
   base::TimeTicks last_success_time_;
 
-  // Is set to true on the internal AUHAL IO thread in the first input callback
-  // after Start() has bee called.
+  // Flags to indicate if we have gotten an input callback.
+  // |got_input_callback_| is only accessed on the OS audio thread in
+  // OnDataIsAvailable() and is set to true when the first callback comes. It
+  // acts as a gate to only set |input_callback_is_active_| atomically once.
+  // |got_input_callback_| is reset to false in Stop() on the main thread. This
+  // is safe since after stopping the audio unit there is no current callback
+  // ongoing and no further callbacks coming.
+  bool got_input_callback_;
   base::subtle::Atomic32 input_callback_is_active_;
 
   // Timer which triggers CheckInputStartupSuccess() to verify that input
@@ -301,30 +294,6 @@ class MEDIA_EXPORT AUAudioInputStream
   UInt32 largest_glitch_frames_;
   int glitches_detected_;
 
-  // Timer that provides periodic callbacks used to monitor if the input stream
-  // is alive or not.
-  std::unique_ptr<base::RepeatingTimer> check_alive_timer_;
-
-  // Time tick set once in each input data callback. The time is measured on
-  // the real-time priority I/O thread but this member is modified and read
-  // on the main thread only.
-  base::TimeTicks last_callback_time_;
-
-  // Counts number of times we get a signal of that a restart seems required.
-  // If it is above a threshold (kNumberOfIndicationsToTriggerRestart), the
-  // current audio stream is closed and a new (using same audio parameters) is
-  // started.
-  size_t number_of_restart_indications_;
-
-  // Counts number of times RestartAudio() has been called. The max number of
-  // attempts is restricted by |kMaxNumberOfRestartAttempts|.
-  // Note that this counter is reset to zero after each successful restart.
-  size_t number_of_restart_attempts_;
-
-  // Counts the total number of times RestartAudio() has been called. It is
-  // set to zero once in the constructor and then never reset again.
-  size_t total_number_of_restart_attempts_;
-
   // Callback to send statistics info.
   AudioManager::LogCallback log_callback_;