Adding new histograms for other devices on hisgtory page.

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 1864 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="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.
   </summary>
 </histogram>
 
 <histogram name="HttpCache.OfflineStatus" enum="OfflineStatus">
   <summary>
     Result of a main page HttpCacheTransaction if offline mode had been enabled.
   </summary>
@@ skipping 12045 matching lines @@
   <int value="12" label="Clicked to other NTP pane."/>
   <int value="13" label="Other action"/>
 </enum>
 
 <enum name="NtpOtherSessionsType" type="int">
   <int value="0" label="Menu initialized"/>
   <int value="1" label="Menu shown"/>
   <int value="2" label="Link clicked"/>
   <int value="3" label="Link context menu shown"/>
   <int value="4" label="Device context menu shown"/>
+<!-- value 5 is NOT used anymore -->

[Alexei Svitkine (slow), 2013/05/31 22:50:03]

Was it used before? If so I think you should add it with maybe (obsolete) at the
end of the description. (In case there are old clients that report this.)

[MAD, 2013/06/01 00:24:01]

Done.

+
+  <int value="6" label="Collapse Session"/>
+  <int value="7" label="Expand Session"/>
+  <int value="8" label="Open All"/>
 </enum>
 
 <enum name="NtpPaneType" type="int">
   <int value="1" label="MostVisited"/>
   <int value="2" label="Apps"/>
   <int value="3" label="Bookmarks"/>
   <int value="4" label="Suggestions"/>
 </enum>
 
 <enum name="NtpPromoAction" type="int">
@@ skipping 2972 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>