Add UMA to count the number of Google CAPTCHA pages shown and solved by users.

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 immediatly after a user takes the
@@ skipping 3395 matching lines @@
 <action name="Gesture_Overview">
   <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="Go">
   <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="GoogleCaptchaShown">

[Alexei Svitkine (slow), 2015/11/13 17:45:12]

I think it would be better to use an enum histogram for this, rather than user
actions. One bucket for shown and the other for solved.

(We have better support for histograms in our dashboards which allow more
powerful analyses.)

[Matt Welsh, 2015/11/13 19:37:16]

Done.

+  <owner>mdw@chromium.org</owner>
+  <description>
+    User visited a page that resulted in a Google CAPTCHA challenge.
+  </description>
+</action>
+
+<action name="GoogleCaptchaSolved">
+  <owner>mdw@chromium.org</owner>
+  <description>User solved a Google CAPTCHA challenge.</description>
+</action>
+
 <action name="GoogleNow.ButtonClicked0">
   <owner>robliao@chromium.org</owner>
   <owner>skare@chromium.org</owner>
   <description>
     User clicked button index 0 (0-based) of a Now Notification.
   </description>
 </action>
 
 <action name="GoogleNow.ButtonClicked1">
   <owner>robliao@chromium.org</owner>
@@ skipping 9695 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>