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

chrome/browser/media/router/route_request_result.h

 // Copyright 2016 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.
 
 #ifndef CHROME_BROWSER_MEDIA_ROUTER_ROUTE_REQUEST_RESULT_H_
 #define CHROME_BROWSER_MEDIA_ROUTER_ROUTE_REQUEST_RESULT_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 12 matching lines @@
 //     be unique.
 // |error|: Empty string.
 // |result_code|: RouteRequestResult::OK
 // On failure:
 // |route|: nullptr
 // |presentation_id|: Empty string.
 // |error|: Non-empty string describing the error.
 // |result_code|: A value from RouteRequestResult describing the error.
 class RouteRequestResult {
  public:
+  // Keep in sync with:
+  // - RouteRequestResultCode in media_router.mojom
+  // - MediaRouteProviderResult enum in tools/metrics/histograms.xml

[Ilya Sherman, 2016/07/18 22:56:57]

Please also document that this enum should be treated as append-only, in order
to back a histogram.

+  // - mr.RouteRequestResultCode in route_request_error.js
   enum ResultCode {
-    UNKNOWN_ERROR,
-    OK,
-    TIMED_OUT,
-    ROUTE_NOT_FOUND,
-    INVALID_ORIGIN,
-    OFF_THE_RECORD_MISMATCH
+    UNKNOWN_ERROR = 0,
+    OK = 1,
+    TIMED_OUT = 2,
+    ROUTE_NOT_FOUND = 3,
+    SINK_NOT_FOUND = 4,
+    INVALID_ORIGIN = 5,
+    OFF_THE_RECORD_MISMATCH = 6,
+    NO_SUPPORTED_PROVIDER = 7,
+
+    // This is the total number of values.
+    TOTAL_COUNT = 8
   };
 
   static std::unique_ptr<RouteRequestResult> FromSuccess(
       std::unique_ptr<MediaRoute> route,
       const std::string& presentation_id);
   static std::unique_ptr<RouteRequestResult> FromError(const std::string& error,
                                                        ResultCode result_code);
 
   ~RouteRequestResult();
 
@@ skipping 14 matching lines @@
   std::string presentation_id_;
   std::string error_;
   ResultCode result_code_;
 
   DISALLOW_COPY_AND_ASSIGN(RouteRequestResult);
 };
 
 }  // namespace media_router
 
 #endif  // CHROME_BROWSER_MEDIA_ROUTER_ROUTE_REQUEST_RESULT_H_