Field trial removing tiles from NTP if URL is already open - for 1993 clients

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 7160 matching lines @@
 </histogram>
 
 <histogram name="NewTabPage.MostVisitedAction" enum="NtpFollowAction">
   <summary>
     Action taken by the user on the Most Visited NTP pane.  If the user switches
     panes during this use of the NTP, this action is sometimes not recorded. Ask
     mpearson@ for details.
   </summary>
 </histogram>
 
+<histogram name="NewTabPage.MostVisitedTilePlacementExperiment"
+    enum="NtpTileExperimentActions">
+  <summary>
+    Histogram of actions carried out by Most Visited Tile Placement experiment.

[beaudoin, 2013/06/20 21:55:44]

This could be a bit more detailed. As such, it's unclear what this is for.
Explain that we want to identify the cases where the experiment could not
operate as expected and the reason for it.

[annark1, 2013/07/04 18:29:15]

Done.

+  </summary>
+</histogram>
+
 <histogram name="NewTabPage.NonVisibleScreenshots">
   <summary>
     The number of screenshots that were cached for the non-visible but ranked
     suggestions on the Suggested NTP pane.
   </summary>
 </histogram>
 
 <histogram name="NewTabPage.NonVisibleSuggestedSiteRank">
   <summary>
     Given that the user has typed a URL, and given that that specific URL was
@@ skipping 8679 matching lines @@
   <int value="3" label="Bookmarks"/>
   <int value="4" label="Suggestions"/>
 </enum>
 
 <enum name="NtpPromoAction" type="int">
   <int value="0" label="NTP Promo viewed"/>
   <int value="1" label="NTP Promo closed"/>
   <int value="2" label="NTP Promo link clicked"/>
 </enum>
 
+<enum name="NtpTileExperimentActions" type="int">
+  <summary>
+    The types of actions performed by the Most Visited Tile Placement experiment

[beaudoin, 2013/06/20 21:55:44]

Same here, a bit more details.

[annark1, 2013/07/04 18:29:15]

Done.

+  </summary>
+  <int value="0" label="Removed URL that was already open in browser"/>
+  <int value="1" label="Didn't remove URL, too few suggestions in MV"/>
+  <int value="2" label="Too few URLs, didn't flip tiles 1 and 8"/>
+  <int value="3" label="Too few URLs, didn't flip tiles 1 and 4"/>
+  <int value="4" label="No URL, couldn't flip any tiles"/>
+</enum>
+
 <enum name="OfflineStatus" type="int">
   <int value="0" label="Fresh data load from Cache"/>
   <int value="1" label="Successful network request (validation or fetch)."/>
   <int value="2" label="Failed network request (non-offline error)."/>
   <int value="3" label="Server offline and stale data available."/>
   <int value="4" label="Server offline and stale data not available."/>
 </enum>
 
 <enum name="OmniboxAggressiveHistoryURLProviderFieldTrialBeacon" type="int">
   <int value="0" label="disabled by flags"/>
@@ skipping 3034 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>