Added UMA metrics for screen capture 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 13882 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_ScreenCapture_Stopped_Default">
+  <owner>bruthig@chromium.org</owner>
+  <owner>tbuckley@chromium.org</owner>
+  <description>
+    Counts the number of times the user stops screen capturing via the default
+    &quot;Screen Capture&quot; view in the system menu.

[tdanderson, 2016/07/07 21:54:31]

nit: remove quotes

Consider rewording for clarity: "... via the screen capture row in the system
menu" or "... via the screen capture row's stop button in the system menu"

[bruthig, 2016/07/08 14:26:53]

Done.

+  </description>
+</action>
+
+<action name="StatusArea_ScreenCapture_Stopped_Notification">
+  <owner>bruthig@chromium.org</owner>
+  <owner>tbuckley@chromium.org</owner>
+  <description>
+    Counts the number of times the user stops screen capturing via the &quot;
+    Screen Capture&quot; notification.

[tdanderson, 2016/07/07 21:54:31]

nit: remove quotes

Is this notification part of the notifications center, or is it one of those
standalone pre-notification-center "notifications" ? May be worth clarifying
here if, for instance, this action ever gets used to measure something related
to the notification center as a whole.

[bruthig, 2016/07/08 14:26:53]

Done.

+  </description>
+</action>
+
 <action name="StatusArea_SignOut">
   <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_SpokenFeedbackDisabled">
   <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>
 
@@ skipping 1046 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>