Add metric to record users opening a new NTP.

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.
 
@@ skipping 9943 matching lines @@
     Deprecated as of 01/2017. Replaced with
     MobileRecentTabManagerTabFromOtherDeviceOpened.
   </obsolete>
 </action>
 
 <action name="MobileNTPMostVisited">
   <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="MobileNTPOpenedInNewTab">
+  <owner>fhorschig@chromium.org</owner>
+  <description>
+    The user manually created a New Tab Page (NTP) in a new tab that has not
+    been shown before. This includes the initial tab (when starting Chrome).
+  </description>
+</action>
+
 <action name="MobileNTPRecentlyClosed">
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <description>Please enter the description of this user action.</description>
   <obsolete>
     Deprecated as of 01/2017. Replaced with
     MobileRecentTabManagerRecentTabOpened.
   </obsolete>
 </action>
 
 <action name="MobileNTPShown">
@@ skipping 6546 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>