Add UserAction when the user opens ReadingList

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 9699 matching lines @@
   <owner>aurimas@chromium.org</owner>
   <description>User pressed 'Print' in the app menu.</description>
 </action>
 
 <action name="MobileMenuQuit">
   <owner>aurimas@chromium.org</owner>
   <description>User pressed 'Quit' in the app menu.</description>
   <obsolete>This menu item was never added to the app menu.</obsolete>
 </action>
 
+<action name="MobileMenuReadingList">
+  <owner>gambard@chromium.org</owner>
+  <description>User pressed 'Reading List' in the app menu.</description>
+</action>
+
 <action name="MobileMenuRecentTabs">
   <owner>justincohen@chromium.org</owner>
   <description>User pressed 'Recent tabs' in the app menu.</description>
 </action>
 
 <action name="MobileMenuReload">
   <owner>tedchoc@chromium.org</owner>
   <description>
     User pressed the reload option in the app menu.  This was added in M55.
     Prior to M55, the menu reload counts were combined with the toolbar counts,
@@ skipping 6616 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>