Record ChromeVox metrics

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 7e94067119120cef98b3dccc797d9749476a9be2..51a1fccc6baa6670cd5aa1a74c3dc2ee380c45ed 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -113,6 +113,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Accessibility.CrosChromeVoxNext" enum="BooleanEnabled">
+  <owner>dmazzoni@chromium.org</owner>
+  <summary>
+    Set when a Chrome OS user has spoken feedback enabled and is using
+    &quot;ChromeVox Next&quot;, a new ChromeVox experience that became the
+    default in Chrome 56 (but can be toggled on or off by the user). Recorded
+    once each time ChromeVox starts up.

[Ilya Sherman, 2016/11/16 23:14:47]

Thanks, this is much clearer to me!  I still have one point of confusion: there
are two conditions listed in the first sentence: (1) spoken feedback must be
enabled, and (2) the user must be using ChromeVox Next.  I *think* that this
histogram is only emitted if (1) is true, and records whether (2) is true.  But,
I could also interpret this as meaning that the histogram is recorded even when
(1) is false, and the output value records whether either (1) or (2) (or both)
were false.  Could you please clarify the phrasing a bit to make this
distinction clearer?

[dmazzoni, 2016/11/16 23:39:08]

Ah, that makes sense.

Clarified.

+  </summary>
+</histogram>
+
 <histogram name="Accessibility.CrosCursorHighlight" enum="BooleanEnabled">
   <owner>dmazzoni@chromium.org</owner>
   <summary>