Add a histogram for recording content suggestions local usage time stats.

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 5f127885cb7c1c36733800e680c138f6f2e724f3..047c6072d4fca6b5607db56166d9b0197a77b2ca 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -37610,6 +37610,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="NewTabPage.ContentSuggestions.UsageTimeLocal">
+  <owner>markusheintz@chromium.org</owner>
+  <summary>
+    Android: The time of day (in the local timezone) when the user used content
+    suggestions. Recorded when the user scrolls below the fold to look at
+    suggestions, at most once per NTP.

[Marc Treib, 2016/11/16 16:14:02]

Not accurate anymore, since it's also recorded for clicks.

[Marc Treib, 2016/11/16 16:14:32]

Ah, already addressed now :)

+  </summary>
+</histogram>
+
 <histogram name="NewTabPage.ContentSuggestions.VisitDuration" units="ms">
   <owner>treib@chromium.org</owner>
   <summary>