System MR2: Add MediaRouter2#registerRouteCallback(executor, callback)

This CL adds registerCallback(executor, callback) as @SystemApi
for system MediaRouter2.

Bug: 183453134
Test: Passed CTS
Change-Id: I50e942714946ae8af7ad69432cefcd8015040d4d

core/api/system-current.txt

@@ -5228,6 +5228,7 @@ package android.media {
     method @Nullable public String getClientPackageName();
     method @Nullable public android.media.MediaRouter2.RoutingController getController(@NonNull String);
     method @Nullable public static android.media.MediaRouter2 getInstance(@NonNull android.content.Context, @NonNull String);
+    method public void registerRouteCallback(@NonNull java.util.concurrent.Executor, @NonNull android.media.MediaRouter2.RouteCallback);
     method public void setRouteVolume(@NonNull android.media.MediaRoute2Info, int);
     method public void startScan();
     method public void stopScan();

media/java/android/media/MediaRouter2.java

@@ -298,6 +298,24 @@ public final class MediaRouter2 {
         return mClientPackageName;
     }
 
+    /**
+     * Registers a callback to receive route related events when they change.
+     * <p>
+     * If the specified callback is already registered, its registration will be updated for the
+     * given {@link Executor executor}.
+     * <p>
+     * This will be no-op for non-system routers.
+     * @hide
+     */
+    @SystemApi
+    public void registerRouteCallback(@NonNull @CallbackExecutor Executor executor,
+            @NonNull RouteCallback routeCallback) {
+        if (!isSystemRouter()) {
+            return;
+        }
+        registerRouteCallback(executor, routeCallback, RouteDiscoveryPreference.EMPTY);
+    }
+
     /**
      * Registers a callback to discover routes and to receive events when they change.
      * <p>