Remove source icon when a corresponding window is activated

Source icons are no longer needed to inform the user about events
having occured in a particular application when (s)he activates the
window - treat that case just as if the user had clicked the source
icon.

https://bugzilla.gnome.org/show_bug.cgi?id=610494

js/ui/messageTray.js

@@ -489,6 +489,12 @@ MessageTray.prototype = {
         }
     },
 
+    removeSourceByApp: function(app) {
+        for (let source in this._sources)
+            if (this._sources[source].app == app)
+                this.removeSource(this._sources[source]);
+    },
+
     removeNotification: function(notification) {
         if (this._notification == notification && (this._notificationState == State.SHOWN || this._notificationState == State.SHOWING)) {
             if (this._notificationTimeoutId) {