Add UMA stats for silence AudioInputController.

media/audio/audio_input_controller.cc

Index: media/audio/audio_input_controller.cc
diff --git a/media/audio/audio_input_controller.cc b/media/audio/audio_input_controller.cc
index 490c62b3c16df6794d1ff6d17d18147f9c759a2c..dee7412df9f95beeb21b2b38f88f42b2a6b98163 100644
--- a/media/audio/audio_input_controller.cc
+++ b/media/audio/audio_input_controller.cc
@@ -63,6 +63,10 @@ AudioInputController::AudioInputController(EventHandler* handler,
       sync_writer_(sync_writer),
       max_volume_(0.0),
       user_input_monitor_(user_input_monitor),
+#if defined(AUDIO_POWER_MONITORING)
+      last_audio_level_was_silence_(false),
+      silence_counter_(0),
+#endif
       prev_key_down_count_(0) {
   DCHECK(creator_task_runner_.get());
 }
@@ -203,6 +207,8 @@ void AudioInputController::DoCreate(AudioManager* audio_manager,
       params.sample_rate(),
       TimeDelta::FromMilliseconds(kPowerMeasurementTimeConstantMilliseconds)));
   audio_params_ = params;
+  last_audio_level_was_silence_ = false;
+  silence_counter_ = 0;
 #endif
 
   // TODO(miu): See TODO at top of file.  Until that's resolved, assume all
@@ -307,6 +313,14 @@ void AudioInputController::DoClose() {
   if (user_input_monitor_)
     user_input_monitor_->DisableKeyPressMonitoring();
 
+#if defined(AUDIO_POWER_MONITORING)
+  // Send UMA stats if we have enabled power monitoring.
+  if (audio_level_) {
+    UMA_HISTOGRAM_COUNTS_10000("Media.AudioInputControllerSilenceCount",
+                               silence_counter_);
+  }
+#endif
+
   state_ = CLOSED;
 }
 
@@ -474,8 +488,14 @@ void AudioInputController::DoLogAudioLevel(float level_dbfs) {
   std::string log_string = base::StringPrintf(
       "AIC::OnData: average audio level=%.2f dBFS", level_dbfs);
   static const float kSilenceThresholdDBFS = -72.24719896f;
-  if (level_dbfs < kSilenceThresholdDBFS)
+  if (level_dbfs < kSilenceThresholdDBFS) {
     log_string += " <=> no audio input!";
+    if (!last_audio_level_was_silence_)
+      ++silence_counter_;
+    last_audio_level_was_silence_ = true;
+  } else {
+    last_audio_level_was_silence_ = false;
+  }
 
   handler_->OnLog(this, log_string);
 #endif