UMA stats for browser/renderer audio rendering buffer size mismatch.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 1e85229ab2098cb3036c58fc450a568310f3df3b..e72160344c6144da24b5d80ee3f86b05f9041fa4 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -21868,6 +21868,23 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Media.Audio.Render.BufferSizeMismatch">
+  <owner>olka@chromium.org</owner>
+  <summary>
+    Mismatch between the system buffer size the browser side renders audio at
+    and the buffer size it requests from renderer.  When equals zero, it means
+    buffer sizes are equal. When positive, the value reflects the average number
+    of extra consecutive render requests issued by browser to renderer
+    (multiplied by 100); any positive values can cause problems for RTC. When
+    negative, it reflects the average number of extra system audio render calls
+    per one request to the renderer (multiplied by 100). Any values those are

[Henrik Grunell, 2016/08/25 12:52:09]

Nit: We had this discussion before :) I believe s/those/that - it's a
conjunction and not a pronoun afaict. Other reviewers can pitch in on this.

+    not multiples of 100 mean that from time to time browser skips a call to
+    renderer, which can cause problems for RTC. The fractional part of the
+    mismatch (i.e. the last two digits of the value) indirectly reflect
+    periodicy of the mismatch effect.
+  </summary>
+</histogram>
+
 <histogram name="Media.Audio.Render.FramesRequested" units="frames">
   <owner>tommi@chromium.org</owner>
   <summary>
@@ -97297,6 +97314,14 @@ To add a new entry, add it with any value and run test to compute valid value.
   <affected-histogram name="DefaultBrowser.SetDefaultAsyncDuration"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="AudioLatency" separator=".">
+  <suffix name="LatencyExactMs" label="Exact latency in milliseconds"/>
+  <suffix name="LatencyInteractive" label="Interactive latency"/>
+  <suffix name="LatencyRtc" label="RTC latency"/>
+  <suffix name="LatencyPlayback" label="Playback latency"/>
+  <affected-histogram name="Media.Audio.Render.BufferSizeMismatch"/>
+</histogram_suffixes>
+
 <histogram_suffixes name="AutofillDataAvailability" separator=".">
   <suffix name="WithNoData" label="no autofill data"/>
   <suffix name="WithOnlyServerData" label="only server autofill data"/>