Adding tools menu responsiveness 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 d1800f8261a89d2e3f42ae6331697e1debe91683..3e719a0dfbf3a7684786dfb24292ea12b30b12fd 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -76261,6 +76261,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="UI.Performance.ShowToolsMenuResponsiveness" units="ms">
+  <owner>peterlaurens@chromium.org</owner>
+  <summary>
+    Number of milliseconds passed between the event that triggers the
+    presentation of the tools menu, and the actual appearance of the menu on

[Ilya Sherman, 2017/05/18 03:00:25]

Which tools menu does this refer to?  Would it make sense to place this
histogram under the "Toolbar" top-level category?  That seems to be where the
code lives.

[PL, 2017/05/18 23:36:34]

Good idea! This is the main menu of controls for Bling, accessed by the three
dot menu in the navigation bar. However our tools menu could exist separately
from a toolbar type object (although the main (only?) way to trigger it is
through a tap on a button in the toolbar).

Looking at the other Toolbar.* items, there's this one:

Toolbar.AppMenuTimeToAction

... which seems to be similar (but not identical) to the type of metric we want
to capture, so maybe it's ok.

Would you then suggest a name like:

"Toolbar.ShowToolsMenuResponsiveness" ?

Thanks!

+    screen. Includes the animation duration.
+  </summary>
+</histogram>
+
 <histogram name="UKM.ActualLogUploadInterval" units="minutes">
   <owner>holte@chromium.org</owner>
   <owner>rkaplow@chromium.org</owner>