fix(messaging): improve typings for Messaging methods

Author: jsayol

typings/app.d.ts

@@ -312,8 +312,8 @@ declare namespace firebase.messaging {
   interface Messaging {
     deleteToken (token : string ) : firebase.Promise < any > | null ;
     getToken ( ) : firebase.Promise < any > | null ;
-    onMessage (nextOrObserver : firebase.Observer<Object, void> ) : ( ) => any ;
-    onTokenRefresh (nextOrObserver : firebase.Observer<Object, void> ) : ( ) => any ;
+    onMessage (nextOrObserver : firebase.Observer<Object, void> | ((payload: Object) => any) ) : ( ) => any ;
+    onTokenRefresh (nextOrObserver : firebase.Observer<Object, void> | ((a: Object) => any) ) : ( ) => any ;
     requestPermission ( ) : firebase.Promise < any > | null ;
     setBackgroundMessageHandler (callback : (a : Object ) => any ) : any ;
     useServiceWorker (registration : any ) : any ;

typings/firebase.d.ts

@@ -312,8 +312,8 @@ declare namespace firebase.messaging {
   interface Messaging {
     deleteToken (token : string ) : firebase.Promise < any > | null ;
     getToken ( ) : firebase.Promise < any > | null ;
-    onMessage (nextOrObserver : firebase.Observer<Object, void> ) : ( ) => any ;
-    onTokenRefresh (nextOrObserver : firebase.Observer<Object, void> ) : ( ) => any ;
+    onMessage (nextOrObserver : firebase.Observer<Object, void> | ((payload: Object) => any) ) : ( ) => any ;
+    onTokenRefresh (nextOrObserver : firebase.Observer<Object, void> | ((a: Object) => any) ) : ( ) => any ;
     requestPermission ( ) : firebase.Promise < any > | null ;
     setBackgroundMessageHandler (callback : (a : Object ) => any ) : any ;
     useServiceWorker (registration : any ) : any ;