Track fraction of visits to top URLs.

tools/metrics/histograms/histograms.xml

 <!--
 Copyright 2013 The Chromium Authors. All rights reserved.
 Use of this source code is governed by a BSD-style license that can be
 found in the LICENSE file.
 -->
 
 <!--
 This file is used to generate a comprehensive list of Chrome histograms along
 with a detailed description for each histogram.
 
@@ skipping 2588 matching lines @@
   <summary>
     Number of total files (regualr files + hosted documents) on Drive.  Logged
     when Drive is first accessed.
   </summary>
 </histogram>
 
 <histogram name="GoogleNow.Event" enum="GoogleNowEvent">
   <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
     to access tabs from other devices.
   </summary>
 </histogram>
 
 <histogram name="HttpCache.EntryLockWait" units="milliseconds">
   <summary>
     The time spent waiting for write lock on a disk cache entry.
@@ skipping 15566 matching lines @@
   <group name="Disabled" label="Neither extra webstore link is visible"/>
   <group name="FooterLink" label="Link in bottom right of footer"/>
   <group name="PlusIcon" label="Plus icon in apps page"/>
   <affected-histogram name="Extensions.AppLaunch"/>
   <affected-histogram name="NewTabPage.DefaultPageType"/>
 </fieldtrial>
 
 </fieldtrials>
 
 </histogram-configuration>