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 8910 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>
+    Records anomalous events for the Most Visited Tile Placement experiment,
+    where it is unable to operate as expected. These are recorded during New Tab
+    Page load time, once for every NTP.
+  </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 10569 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, used to identify the cases where the experiment could not
+    operate as expected, and the reason for it.
+  </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"/>
+</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 4181 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>