Add 24000KHz support to the uma stat.

https://codereview.chromium.org/554733002 added support to 24K as sample rate, we need to update the uma stat correspondingly.

BUG=411241

Review URL: https://codereview.chromium.org/602503003

Cr-Commit-Position: refs/heads/master@{#296419}

tools/metrics/histograms/histograms.xml

@@ -38519,6 +38519,7 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="8" label="k88200Hz"/>
   <int value="9" label="k176400Hz"/>
   <int value="10" label="k192000Hz"/>
+  <int value="11" label="k24000Hz"/>
 </enum>
 
 <enum name="AudioTrackProcessingStates" type="int">