ui: Cleanup class/struct forward declarations

media/blink/webmediaplayer_cast_android.cc

Index: media/blink/webmediaplayer_cast_android.cc
diff --git a/media/blink/webmediaplayer_cast_android.cc b/media/blink/webmediaplayer_cast_android.cc
index 847428d2f20e998eed59b6902682908fd1ab9084..22dcbb700e152d84b8b771fec3fa6c213d0bf2c2 100644
--- a/media/blink/webmediaplayer_cast_android.cc
+++ b/media/blink/webmediaplayer_cast_android.cc
@@ -302,6 +302,10 @@ void WebMediaPlayerCast::OnCancelledRemotePlaybackRequest() {
   client_->cancelledRemotePlaybackRequest();
 }
 
+void WebMediaPlayerCast::OnRemotePlaybackStarted() {
+  client_->remotePlaybackStarted();
+}
+
 void WebMediaPlayerCast::OnDidExitFullscreen() {
   DVLOG(1) << __FUNCTION__;
 }