Add Media.AudioRendererEvents histogram to measure how often OnRenderError() is called.

tools/metrics/histograms/histograms.xml

 <!--
 Copyright 2013 The Chromium Authors. All rights reserved.
 Use of this source code is governed by a BSD-style license that can be
 found in the LICENSE file.
 -->
 
 <!--
 This file is used to generate a comprehensive list of Chrome histograms along
 with a detailed description for each histogram.
 
@@ skipping 759 matching lines @@
   <summary>
     Time Non-IDB LevelDBEnv slept before successfully completing this operation.
     0 means success on the first try.
   </summary>
 </histogram>
 
 <histogram name="Linux.GlibcVersion" enum="LinuxGlibcVersion">
   <summary>The version of glibc used. (Linux only)</summary>
 </histogram>
 
+<histogram name="Media.AudioRendererEvents" enum="AudioRendererEvents">
+  <summary>Captures statistics for various AudioRendererImpl events.</summary>
+</histogram>
+
 <histogram name="Media.DetectedAudioCodec" enum="FFmpegCodecs">
   <summary>Audio codec used in HTML5 media.</summary>
 </histogram>
 
 <histogram name="Media.DetectedVideoCodec" enum="FFmpegCodecs">
   <summary>Video codec used in HTML5 media.</summary>
 </histogram>
 
 <histogram name="Media.VAVDAH264.DecoderFailure" enum="VAVDAH264DecoderFailure">
   <summary>
@@ skipping 3345 matching lines @@
 
 <!-- Enum types -->
 
 <enums>
 
 <enum name="Abandoned" type="int">
   <int value="0" label="Finished"/>
   <int value="1" label="Abandoned"/>
 </enum>
 
+<enum name="AudioRendererEvents" type="int">
+  <int value="0" label="Initialized"/>
+  <int value="1" label="Runtime error"/>
+</enum>
+
 <enum name="AutocheckoutBubble" type="int">
   <int value="0" label="Created"/>
   <int value="1" label="Accepted"/>
   <int value="2" label="Dismissed"/>
   <int value="3" label="Ignored"/>
   <int value="4" label="Could be displayed"/>
 </enum>
 
 <enum name="AutocheckoutBuyFlow" type="int">
   <int value="0" label="Started"/>
@@ skipping 3766 matching lines @@
 <fieldtrial name="SSLResumption">
   <group name="Resume_Handshake" label="Session Resumption"/>
   <group name="Full_Handshake" label="Full"/>
   <affected-histogram name="Net.SSL_Connection_Latency"/>
   <affected-histogram name="Net.SSL_Connection_Latency_Google"/>
 </fieldtrial>
 
 </fieldtrials>
 
 </histogram-configuration>