Emit NotificationClosed for a notification iff we destroy it

This fixes emitting NotificationClosed for resident notifications
that are clicked, but are not actually destroyed.

This also ensures that we emit NotificationClosed in all cases when
a notification is destroyed, which can happen when:
- a non-resident notification is clicked
- an action is invoked on a non-resident notification
- an application the notification was associated with is focused
- a transient notification is done showing
- a notification was requested to be closed by the application
- a tray icon the notification was associated with is removed

https://bugzilla.gnome.org/show_bug.cgi?id=638071

js/ui/messageTray.js

@@ -41,6 +41,17 @@ const State = {
     HIDING:  3
 };
 
+// These reasons are useful when we destroy the notifications received through
+// the notification daemon. We use EXPIRED for transient notifications that the
+// user did not interact with, DISMISSED for all other notifications that were
+// destroyed as a result of a user action, and SOURCE_CLOSED for the notifications
+// that were requested to be destroyed by the associated source.
+const NotificationDestroyedReason = {
+    EXPIRED: 1,
+    DISMISSED: 2,
+    SOURCE_CLOSED 3
+};
+
 // Message tray has its custom Urgency enumeration. LOW, NORMAL and CRITICAL
 // urgency values map to the corresponding values for the notifications received
 // through the notification daemon. HIGH urgency value is used for chats received
@@ -755,8 +766,10 @@ Notification.prototype = {
         }
     },
 
-    destroy: function() {
-        this.emit('destroy');
+    destroy: function(reason) {
+        if (!reason)
+            reason = NotificationDestroyedReason.DISMISSED;
+        this.emit('destroy', reason);
     }
 };
 Signals.addSignalMethods(Notification.prototype);
@@ -1596,7 +1609,7 @@ MessageTray.prototype = {
         let notification = this._notification;
         this._notification = null;
         if (notification.isTransient)
-            notification.destroy();
+            notification.destroy(NotificationDestroyedReason.EXPIRED);
     },
 
     _expandNotification: function(autoExpanding) {
@@ -1746,7 +1759,7 @@ MessageTray.prototype = {
         let summaryNotification = this._summaryNotification;
         this._summaryNotification = null;
         if (summaryNotification.isTransient && !this._reNotifyWithSummaryNotificationAfterHide)
-            summaryNotification.destroy();
+            summaryNotification.destroy(NotificationDestroyedReason.EXPIRED);
         if (this._reNotifyWithSummaryNotificationAfterHide) {
             this._onNotify(summaryNotification.source, summaryNotification);
             this._reNotifyWithSummaryNotificationAfterHide = false;