Add FramesSentAsOverlay UMA metric to AVDA.

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 b9221d9b2dd6c9fb3fae43d47ec44e3d669eba31..e4caa3bbac8506f032a2b64349d0b753a0bdaf96 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -21662,6 +21662,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Media.AVDA.FrameSentAsOverlay" enum="BooleanFrameAsOverlay">
+  <owner>liberato@chromium.org</owner>
+  <summary>
+    Record a count for each frame sent to the client by AVDA.  True counts
+    indicate that the frame was an overlay (SurfaceView).  False counts are for
+    SurfaceTexture frames.
+  </summary>
+</histogram>
+
 <histogram name="Media.AVDA.InputQueueTime" units="ms">
   <owner>watk@chromium.org</owner>
   <obsolete>
@@ -67476,6 +67485,11 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="1" label="Lacks Form Manager"/>
 </enum>
 
+<enum name="BooleanFrameAsOverlay" type="int">
+  <int value="0" label="Frame was allow_overlay"/>
+  <int value="1" label="Frame was not allow_overlay"/>

[Ilya Sherman, 2016/07/20 02:17:04]

These labels seem reversed from what the histogram description says.  Please
double-check to make sure that the boolean logic matches up.

+</enum>
+
 <enum name="BooleanFromAddressBook" type="int">
   <int value="0" label="Not From Address Book"/>
   <int value="1" label="From Address Book"/>