Record how often we end up in Chrome from external navigations.

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 119 matching lines @@
   <parameters num-cohorts="128" bytes="4" hash-functions="2" fake-prob="0.5"
       fake-one-prob="0.5" one-coin-prob="0.75" zero-coin-prob="0.25"
       reporting-level="FINE" noise-level="NORMAL_NOISE"/>
 </rappor-parameters>
 
 </rappor-parameter-types>
 
 <rappor-metrics>
 <!-- Rappor metric definitions -->
 
+<rappor-metric name="Android.ExternalNavigationNotChosen"
+    type="UMA_RAPPOR_TYPE">
+  <owner>mariakhomenko@chromium.org</owner>
+  <summary>
+    The package name of an application that was given as an alternative choice
+    to handling a URL in Chrome, but wasn't chosen.
+  </summary>
+</rappor-metric>
+
 <rappor-metric name="AppBanner.NativeApp.Dismissed" type="ETLD_PLUS_ONE">
   <owner>dfalcantara@chromium.org</owner>
   <summary>
     The eTLD+1 of a URL that displayed a native app banner, which was explicitly
     dismissed by the user.
   </summary>
 </rappor-metric>
 
 <rappor-metric name="AppBanner.NativeApp.Installed" type="ETLD_PLUS_ONE">
   <owner>dfalcantara@chromium.org</owner>
@@ skipping 1877 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>