Added Ash.SystemMenu.DefaultView.VisibleItems histogram.

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 c6367d6f83892ae25eb2cda508e708157a4edf77..48326a96c6cd2e9ec2090d3968bb037099e8cab9 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -1405,6 +1405,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>The duration of mostly stationary long-duration touches.</summary>
 </histogram>
 
+<histogram name="Ash.SystemMenu.DefaultView.VisibleRows" units="rows">

[rkaplow, 2016/07/21 18:34:25]

since this is an enum histogram, you should create an associated enum here so
you have the correct mapping

[bruthig, 2016/07/21 19:03:22]

Done.

+  <owner>bruthig@chromium.org</owner>
+  <owner>tbuckley@chromium.org</owner>
+  <summary>
+    The visible rows displayed in the system menu's default view. Recorded each
+    time the menu is opened.
+  </summary>
+</histogram>
+
 <histogram name="Ash.SystemMenu.PercentageOfWorkAreaHeightCoveredByMenu"
     units="%">
   <owner>tdanderson@chromium.org</owner>