[Media Router] Adds return value to mojo MediaRouteProvider::TerminateRoute.

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 84a0cddca55924ed6434d98513875a9781327b4a..bb44e21ad4dca58dc6c91e27f72d5409b9a7d788 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -23112,6 +23112,12 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>Location the user clicked to open the Media Router dialog.</summary>
 </histogram>
 
+<histogram name="MediaRouter.Provider.TerminateRoute.Result"
+    enum="MediaRouteProviderResult">
+  <owner>mfoltz@chromium.org</owner>
+  <summary>Result of a request to terminate a route.</summary>
+</histogram>
+
 <histogram name="MediaRouter.Provider.Version" enum="MediaRouteProviderVersion">
   <owner>mfoltz@chromium.org</owner>
   <summary>
@@ -82898,6 +82904,15 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="1" label="Has errors"/>
 </enum>
 
+<enum name="MediaRouteProviderResult" type="int">
+  <int value="0" label="UnknownError"/>
+  <int value="1" label="Ok"/>
+  <int value="2" label="TimedOut"/>
+  <int value="3" label="RouteNotFound"/>
+  <int value="4" label="InvalidOrigin"/>
+  <int value="5" label="OffTheRecordMismatch"/>
+</enum>
+
 <enum name="MediaRouteProviderVersion" type="int">
   <int value="0" label="Unknown"/>
   <int value="1" label="SameVersionAsChrome"/>