Added UMA metrics for the system update UI in the status area.

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 13897 matching lines @@
 <action name="StatusArea_Network_WifiDisabled">
   <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="StatusArea_Network_WifiEnabled">
   <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="StatusArea_OS_Update_Default_Selected">
+  <owner>bruthig@chromium.org</owner>
+  <owner>tbuckley@chromium.org</owner>
+  <description>
+    Counts the number of times the user selects the update row in the system
+    menu.
+  </description>
+</action>
+
 <action name="StatusArea_SMS_Detailed">
   <owner>tbuckley@chromium.org</owner>
   <owner>bruthig@chromium.org</owner>
   <description>
     Counts the number of times the user has opened the &quot;SMS messages &quot;
     detailed view in the system menu.
   </description>
 </action>
 
 <action name="StatusArea_SMS_Detailed_DismissMsg">
@@ skipping 1090 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>