[UMA, Android, MediaFling] Record the domain and registry of the frame url when casting.

tools/metrics/rappor/rappor.xml

 <!--
 Copyright 2015 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.
 -->
 
 <rappor-configuration>
 <!--
 This file is used to generate a comprehensive list of Chrome rappor metrics
 along with a detailed description for each histogram. See the design doc at
@@ skipping 124 matching lines @@
   </summary>
 </rappor-metric>
 
 <rappor-metric name="BackgroundSync.Register.Origin" type="UMA_RAPPOR_TYPE">
   <owner>jkarlin@chromium.org</owner>
   <summary>
     The eTLD+1 of a URL which registered a Background Sync event.
   </summary>
 </rappor-metric>
 
+<rappor-metric name="Cast.Sender.MediaFrameUrl" type="ETLD_PLUS_ONE">
+  <owner>avayvod@chromium.org</owner>
+  <owner>aberent@chromium.org</owner>
+  <summary>
+    The domain and registry of the frame URL that the user is trying to cast
+    the media from. Recorded every time the user casts the media.
+  </summary>
+</rappor-metric>
+
 <rappor-metric name="ContentSettings.MixedScript.DisplayedShield"
     type="ETLD_PLUS_ONE">
   <owner>lgarron@chromium.org</owner>
   <summary>
     The eTLD+1 of a URL that displayed a mixed script shield. Note: this does
     *not* include pages with mixed scripts where the user has already clicked
     through the shield.
   </summary>
 </rappor-metric>
 
@@ skipping 1212 matching lines @@
     <flag>Bit 1: IS_REPEAT_VISIT</flag>
     <summary>
       Bitfield of the state from an SSL warning interstitial.
     </summary>
   </flags-field>
 </rappor-metric>
 
 </rappor-metrics>
 
 </rappor-configuration>