Add @MainThread in MediaRouter.reset()

Bug: 197849017
Test: ./gradlew :mediarouter:mediarouter:lintDebug
Relnote: N/A
Change-Id: I53d6522f0139a23e144fbc7b4c21ae6f7765abfe

diff --git a/mediarouter/mediarouter/api/current.txt b/mediarouter/mediarouter/api/current.txt
index c47a66d..8a418aa4 100644
--- a/mediarouter/mediarouter/api/current.txt
+++ b/mediarouter/mediarouter/api/current.txt

@@ -354,7 +354,7 @@
     method public void removeCallback(androidx.mediarouter.media.MediaRouter.Callback);
     method public void removeProvider(androidx.mediarouter.media.MediaRouteProvider);
     method public void removeRemoteControlClient(Object);
-    method @VisibleForTesting public static void reset();
+    method @MainThread @VisibleForTesting public static void reset();
     method public void selectRoute(androidx.mediarouter.media.MediaRouter.RouteInfo);
     method public void setMediaSession(Object?);
     method public void setMediaSessionCompat(android.support.v4.media.session.MediaSessionCompat?);

diff --git a/mediarouter/mediarouter/api/public_plus_experimental_current.txt b/mediarouter/mediarouter/api/public_plus_experimental_current.txt
index c47a66d..8a418aa4 100644
--- a/mediarouter/mediarouter/api/public_plus_experimental_current.txt
+++ b/mediarouter/mediarouter/api/public_plus_experimental_current.txt

@@ -354,7 +354,7 @@
     method public void removeCallback(androidx.mediarouter.media.MediaRouter.Callback);
     method public void removeProvider(androidx.mediarouter.media.MediaRouteProvider);
     method public void removeRemoteControlClient(Object);
-    method @VisibleForTesting public static void reset();
+    method @MainThread @VisibleForTesting public static void reset();
     method public void selectRoute(androidx.mediarouter.media.MediaRouter.RouteInfo);
     method public void setMediaSession(Object?);
     method public void setMediaSessionCompat(android.support.v4.media.session.MediaSessionCompat?);

diff --git a/mediarouter/mediarouter/api/restricted_current.txt b/mediarouter/mediarouter/api/restricted_current.txt
index c47a66d..8a418aa4 100644
--- a/mediarouter/mediarouter/api/restricted_current.txt
+++ b/mediarouter/mediarouter/api/restricted_current.txt

@@ -354,7 +354,7 @@
     method public void removeCallback(androidx.mediarouter.media.MediaRouter.Callback);
     method public void removeProvider(androidx.mediarouter.media.MediaRouteProvider);
     method public void removeRemoteControlClient(Object);
-    method @VisibleForTesting public static void reset();
+    method @MainThread @VisibleForTesting public static void reset();
     method public void selectRoute(androidx.mediarouter.media.MediaRouter.RouteInfo);
     method public void setMediaSession(Object?);
     method public void setMediaSessionCompat(android.support.v4.media.session.MediaSessionCompat?);

diff --git a/mediarouter/mediarouter/src/main/java/androidx/mediarouter/media/MediaRouter.java b/mediarouter/mediarouter/src/main/java/androidx/mediarouter/media/MediaRouter.java
index 617daf6..88038c2 100644
--- a/mediarouter/mediarouter/src/main/java/androidx/mediarouter/media/MediaRouter.java
+++ b/mediarouter/mediarouter/src/main/java/androidx/mediarouter/media/MediaRouter.java

@@ -309,7 +309,9 @@
      *     <li>{@link androidx.mediarouter.app.MediaRouteControllerDialog}
      *     <li>{@link androidx.mediarouter.app.MediaRouteDiscoveryFragment}
      * </ul>
+     * Please make sure this is called in the main thread.
      */
+    @MainThread
     @VisibleForTesting
     public static void reset() {
         if (sGlobal == null) {