Log NTP hovers in 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 7748 matching lines @@
 </histogram>
 
 <histogram name="NewTabPage.NonVisibleSuggestedSiteRank">
   <summary>
     Given that the user has typed a URL, and given that that specific URL was
     ranked but not visible on the Suggested pane of the NTP, this is the rank
     that the Suggested pane had for that URL.
   </summary>
 </histogram>
 
+<histogram name="NewTabPage.NumberOfMouseOvers">
+  <summary>
+    The total number of times the user hovered the mouse over Most Visited tile
+    or title elements before changing focus away from the NTP, be it by
+    navigating to a URL, switching tabs, changing the active window or closing
+    the tab/shutting down Chrome. Does not log 0 mouseover cases (for instance
+    if a user opens the NTP then immediately switches to another tab without
+    interacting with that NTPinstance).
+  </summary>
+</histogram>
+
 <histogram name="NewTabPage.OtherSessionsMenu" enum="NtpOtherSessionsType">
   <summary>
     Histogram for usage of the menu on the NTP that allows the user to access
     tabs from other devices.
   </summary>
 </histogram>
 
 <histogram name="NewTabPage.PreviousSelectedPageType" enum="NtpPaneType">
   <summary>
     The pane that had been previously selected when the user switches panes in
@@ skipping 12223 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>