Adds translate infobar impression in the old Translate UI on Android

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 7de5ee9588f25c6f8f38940f6919a63cce2fdb85..71fc9cf9f1f2327514cc24f3acacfca25898a118 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -76440,6 +76440,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Translate.InfobarImpression" enum="Boolean" units="views">

[Ilya Sherman, 2017/05/25 22:24:48]

enum: Please specify "BooleanHit"; or better yet, use a custom enum with a label
like "Infobar shown".

[Ilya Sherman, 2017/05/25 22:24:48]

nit: Perhaps name this "InfobarShown" or "InfobarViewed"?

[Ilya Sherman, 2017/05/25 22:24:48]

nit: Units are not supported on enum histograms (arguably they should be, but we
currently don't have support for them implemented.)

[ramyasharma, 2017/05/26 00:17:42]

Done.

[ramyasharma, 2017/05/26 00:17:42]

Done.

[ramyasharma, 2017/05/26 00:17:42]

Done.

+  <owner>ramyasharma@google.com</owner>
+  <summary>
+    The number of times the translate infobar was shown in the UI on Android.
+    Only true is recorded.
+  </summary>
+</histogram>
+
 <histogram name="Translate.InitiationStatus" enum="TranslateInitiationStatus">
   <obsolete>
     Deprecated as of 11/2013, and replaced by Translate.InitiationStatus.v2.