Track fraction of visits to top URLs.

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 963bb406482ddfc58592ebedcacac87c7eb5a0e2..c64250bde844bfbfdb527869dce13fc146402d07 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -2606,6 +2606,10 @@ other types of suffix sets.
   <summary>Events in Google Now component extension.</summary>
 </histogram>
 
+<histogram name="History.TopSitesVisitsByRank" units="rank">
+  <summary>Page visits to each of a user's top k sites.</summary>

[jar (doing other things), 2013/06/11 00:47:35]

This seems like a strange metric.

Are you saying that the kth bucket will contain a count of the number of times a
user visited the kth ranked site?

Are you trying to estimate what the usage curve looks like?

If so, you certainly need to have the normalization which shows how many visits
were "in the unsung long tail."

Can you verbalize what you're hoping to learn from this??

+</histogram>
+
 <histogram name="HistoryPage.OtherSessionsMenu" enum="NtpOtherSessionsType">
   <summary>
     Histogram for usage of the section in the history page that allows the user