[Android] Add AppMenu touch duration metric.

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 e22ab98ff6c812e948a41928b1116d88fe0b7577..55b64018dc5df0018502f29b9b7ff7bd7548fc2a 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -418,6 +418,13 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="AppMenu.TouchDuration" units="milliseconds">

[Alexei Svitkine (slow), 2014/12/08 15:50:52]

This looks like it's adding a new top-level prefix, which we generally try to
avoid doing too often.

Is there another prefix that this can use? Or do you expect a lot of metrics
being added under this prefix going forward?

[Kibeom Kim (inactive), 2014/12/15 22:14:30]

Done.

+  <owner>kkimlabs@google.com</owner>
+  <summary>
+    Time difference between touch down and touch up on the menu button.

[Alexei Svitkine (slow), 2014/12/08 15:50:52]

Mention that it's Android specific.

[Kibeom Kim (inactive), 2014/12/15 22:14:30]

Done.

+  </summary>
+</histogram>
+
 <histogram name="Apps.AppInfoDialog.Launches" enum="AppInfoDialogLaunchOrigin">
   <owner>sashab@chromium.org</owner>
   <summary>