added uma stats to check the usage of media stream audio track audio processing

content/renderer/media/media_stream_audio_processor.cc

Index: content/renderer/media/media_stream_audio_processor.cc
diff --git a/content/renderer/media/media_stream_audio_processor.cc b/content/renderer/media/media_stream_audio_processor.cc
index 11e889259c0045346b9e5714ade5649ef5aa6fdf..4bd9a0d20fbed31cd30719d4c848aa9827593db8 100644
--- a/content/renderer/media/media_stream_audio_processor.cc
+++ b/content/renderer/media/media_stream_audio_processor.cc
@@ -7,6 +7,7 @@
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/metrics/field_trial.h"
+#include "base/metrics/histogram.h"
 #include "content/public/common/content_switches.h"
 #include "content/renderer/media/media_stream_audio_processor_options.h"
 #include "content/renderer/media/rtc_media_constraints.h"
@@ -34,6 +35,13 @@ const int kAudioProcessingNumberOfChannel = 1;
 
 const int kMaxNumberOfBuffersInFifo = 2;
 
+enum AudioTrackProcessingStates {

[Alexei Svitkine (slow), 2014/03/17 22:15:50]

Nit: Add a comment that this is used for an UMA histograms and entries shouldn't
re-ordered or removed.

[no longer working on chromium, 2014/03/19 12:50:11]

Done.

+  AUDIO_PROCESSING_ENABLED = 0,
+  AUDIO_PROCESSING_DISABLED,
+  AUDIO_PROCESSING_IN_WEBRTC,
+  AUDIO_PROCESSING_MAX
+};
+
 }  // namespace
 
 class MediaStreamAudioProcessor::MediaStreamAudioConverter
@@ -265,8 +273,11 @@ void MediaStreamAudioProcessor::InitializeAudioProcessingModule(
     const blink::WebMediaConstraints& constraints, int effects,
     MediaStreamType type) {
   DCHECK(!audio_processing_);
-  if (!IsAudioTrackProcessingEnabled())
+  if (!IsAudioTrackProcessingEnabled()) {
+    UMA_HISTOGRAM_ENUMERATION("Media.AudioTrackProcessingStates",
+                              AUDIO_PROCESSING_IN_WEBRTC, AUDIO_PROCESSING_MAX);
     return;
+  }
 
   RTCMediaConstraints native_constraints(constraints);
 
@@ -319,6 +330,8 @@ void MediaStreamAudioProcessor::InitializeAudioProcessingModule(
   if (!enable_aec && !enable_experimental_aec && !enable_ns &&
       !enable_high_pass_filter && !enable_typing_detection && !enable_agc &&
       !enable_experimental_ns) {
+    UMA_HISTOGRAM_ENUMERATION("Media.AudioTrackProcessingStates",
+                              AUDIO_PROCESSING_DISABLED, AUDIO_PROCESSING_MAX);
     return;
   }
 
@@ -361,6 +374,9 @@ void MediaStreamAudioProcessor::InitializeAudioProcessingModule(
   CHECK_EQ(audio_processing_->set_num_channels(kAudioProcessingNumberOfChannel,
                                                kAudioProcessingNumberOfChannel),
            0);
+
+  UMA_HISTOGRAM_ENUMERATION("Media.AudioTrackProcessingStates",

[Alexei Svitkine (slow), 2014/03/17 22:15:50]

Nit: Can you make a function in the anon namespace that takes an enum value and
logs this? Each macro use bloats the binary a bit, so it's better to consolidate
ones for the same histogram.

[no longer working on chromium, 2014/03/19 12:50:11]

Done.

+                            AUDIO_PROCESSING_ENABLED, AUDIO_PROCESSING_MAX);
 }
 
 void MediaStreamAudioProcessor::InitializeCaptureConverter(