Add new NTP layout with snippet cards and hide it behind a flag

tools/metrics/actions/actions.xml

 <!--
 Copyright 2014 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 a comprehensive list of Chrome user actions along with the owner
 and description for each user action. A user action should be tied to an actual
 action taken by a user. It should be logged immediately after a user takes the
@@ skipping 8341 matching lines @@
     Android: User scrolled through the snippet cards. Recorded at the beginning
     of the scroll event.
   </description>
 </action>
 
 <action name="MobileNTP.Snippets.ShowLess">
   <owner>knn@chromium.org</owner>
   <description>
     Android: User clicked on a snippet card to hide the bigger summary.
   </description>
+  <obsolete>Deprecated as of 4/2016</obsolete>
 </action>
 
 <action name="MobileNTP.Snippets.ShowMore">
   <owner>knn@chromium.org</owner>
   <description>
     Android: User clicked on a snippet card to reveal a bigger summary.
   </description>
+  <obsolete>Deprecated as of 4/2016</obsolete>
 </action>
 
 <action name="MobileNTPBookmark">
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <description>Please enter the description of this user action.</description>
 </action>
 
 <action name="MobileNTPForeignSession">
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <description>Please enter the description of this user action.</description>
@@ skipping 5665 matching lines @@
 <action name="webapps.AddShortcut.Manifest">
   <owner>mlamouri@chromium.org</owner>
   <description>
     Shortcut added to the homescreen with a valid Manifest. This action will be
     recorded in addition to AppShortcut, AppShortcutApple and Bookmark actions
     to keep a trend of whether the webapp also add meta tags.
   </description>
 </action>
 
 </actions>