Add P2 UMA metrics for Media Router user actions.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 7811dbedc20198f909c085e4afaf6c830e6ac9d7..eac6ae209b3b31fd62766a19d612397bead0af9c 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -19639,6 +19639,12 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="MediaRouter.Ui.Action.StartLocalPosition"
+    enum="MediaRouterSinkPositionLabel">
+  <owner>apacible@chromium.org</owner>
+  <summary>The index of the sink that was selected in the sink list.</summary>
+</histogram>
+
 <histogram name="MediaRouter.Ui.Action.StartLocalSessionSuccessful"
     enum="BooleanSuccess">
   <owner>apacible@chromium.org</owner>
@@ -19647,6 +19653,11 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="MediaRouter.Ui.Action.StopRoute" enum="MediaRouteType">
+  <owner>apacible@chromium.org</owner>
+  <summary>The number of times a user stops different types of routes.</summary>
+</histogram>
+
 <histogram name="MediaRouter.Ui.Device.Count">
   <owner>apacible@chromium.org</owner>
   <summary>
@@ -19671,6 +19682,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="MediaRouter.Ui.Navigate.SourceSelection"
+    enum="MediaRouterSourceTypes">
+  <owner>apacible@chromium.org</owner>
+  <summary>
+    The number of times the user selects a specific cast source type.
+  </summary>
+</histogram>
+
 <histogram name="Memory.BackingStore">
   <owner>hajimehoshi@chromium.org</owner>
   <owner>kenjibaheux@google.com</owner>
@@ -70363,6 +70382,21 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="3" label="Page"/>
 </enum>
 
+<enum name="MediaRouterSinkPositionLabel" type="int">
+  <int value="100" label="100+"/>
+</enum>
+
+<enum name="MediaRouterSourceTypes" type="int">
+  <int value="1" label="App"/>
+  <int value="2" label="Tab"/>
+  <int value="4" label="Desktop"/>
+</enum>
+
+<enum name="MediaRouteType" type="int">
+  <int value="0" label="Local"/>
+  <int value="1" label="Remote"/>
+</enum>
+
 <enum name="MediaSessionActionSource" type="int">
   <int value="0" label="Media Notification"/>
   <int value="1" label="MediaSession (Android)"/>