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 4c1a2c90ab299c27846cebd1c56e730cc9f0f22a..1a5c73fc89bb33722d51162cc7d1605569206e46 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 +35,12 @@ const int kAudioProcessingNumberOfChannel = 1;
 
 const int kMaxNumberOfBuffersInFifo = 2;
 
+enum AudioTrackProcessingStates {
+  AUDIO_PROCESSING_ENABLED = 0,
+  AUDIO_PROCESSING_DISABLED,
+  AUDIO_PROCESSING_MAX
+};
+
 }  // namespace
 
 class MediaStreamAudioProcessor::MediaStreamAudioConverter
@@ -265,8 +272,11 @@ 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_DISABLED, AUDIO_PROCESSING_MAX);
     return;
+  }
 
   RTCMediaConstraints native_constraints(constraints);
 
@@ -319,6 +329,8 @@ 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);

[tommi (sloooow) - chröme, 2014/03/14 14:38:32]

Could we have a different value for this case?

Here we're actually still running the APM in Chrome, but the constraints specify
that no APM should be done (right?).  So I think that by putting this case in
the same bucket as 'disabled' could skew the numbers (as the APM code path is
actually enabled).

Maybe AUDIO_PROCESSING_BYPASSED?

[no longer working on chromium, 2014/03/14 14:43:56]

Do we really want this? AUDIO_PROCESSING_BYPASSED will soon go away, in one
month? And it probably does not tell much.
Note that we can't keep two paths for long, the code has to go away then we can
do a thorough clean up.

     return;
   }
 
@@ -361,6 +373,9 @@ void MediaStreamAudioProcessor::InitializeAudioProcessingModule(
   CHECK_EQ(audio_processing_->set_num_channels(kAudioProcessingNumberOfChannel,
                                                kAudioProcessingNumberOfChannel),
            0);
+
+  UMA_HISTOGRAM_ENUMERATION("Media.AudioTrackProcessingStates",
+                            AUDIO_PROCESSING_ENABLED, AUDIO_PROCESSING_MAX);
 }
 
 void MediaStreamAudioProcessor::InitializeCaptureConverter(