(Not for review) Dummy C++ side Custom Controls implementation

chrome/browser/media/router/mojo/media_router.mojom

Index: chrome/browser/media/router/mojo/media_router.mojom
diff --git a/chrome/browser/media/router/mojo/media_router.mojom b/chrome/browser/media/router/mojo/media_router.mojom
index 37fc064748de40d2a68f17ebec05798d2c3a4871..a7cf206dfc21edbcc44386024af24b8502c22661 100644
--- a/chrome/browser/media/router/mojo/media_router.mojom
+++ b/chrome/browser/media/router/mojo/media_router.mojom
@@ -4,6 +4,7 @@
 
 module media_router.mojom;
 
+import "chrome/browser/media/router/mojo/media_controller.mojom";
 import "mojo/common/time.mojom";
 import "url/mojo/origin.mojom";
 
@@ -322,6 +323,18 @@ interface MediaRouteProvider {
               string media_source,
               SinkSearchCriteria search_criteria) =>
                   (string sink_id);
+
+  // Creates a controller for the media route with given |route_id| and binds it
+  // to |media_controller| for receiving media commands. This method returns
+  // false if such a media route doesn't exist, a controller already exists
+  // for it, or there was an error while creating a controller.
+  // |media_controller| becomes invalid when the media route is terminated. The
+  // created controller is destroyed when |media_controller| becomes invalid.
+  // TODO(takumif): Consider returning an enum instead of a bool to distinguish
+  // between error conditions for metrics/debugging.
+  CreateMediaRouteController(string route_id,
+                             MediaController& media_controller) =>
+                                 (bool success);
 };
 
 // Interface for a service which observes state changes across media