Reduce unnecessary updates on conversations at startup

js/models/conversations.js

@@ -188,12 +188,15 @@
         return collection.fetchConversation(this.id, 1).then(function() {
             var lastMessage = collection.at(0);
             if (lastMessage) {
-              this.save({
+              this.set({
                 lastMessage : lastMessage.getNotificationText(),
                 timestamp   : lastMessage.get('sent_at')
               });
             } else {
-              this.save({ lastMessage: '', timestamp: null });
+              this.set({ lastMessage: '', timestamp: null });
+            }
+            if (this.hasChanged('lastMessage') || this.hasChanged('timestamp')) {
+                this.save();
             }
         }.bind(this));
     },

js/views/conversation_list_item_view.js

@@ -20,10 +20,11 @@
             this.listenTo(this.model, 'change', _.debounce(this.render.bind(this), 1000));
             this.listenTo(this.model, 'destroy', this.remove); // auto update
             this.listenTo(this.model, 'opened', this.markSelected); // auto update
-            this.listenTo(this.model.messageCollection, 'add remove',
-              _.debounce(this.model.updateLastMessage.bind(this.model), 1000));
-            this.listenTo(this.model, 'newmessage',
-              _.debounce(this.model.updateLastMessage.bind(this.model), 1000));
+
+            var updateLastMessage = _.debounce(this.model.updateLastMessage.bind(this.model), 1000);
+            this.listenTo(this.model.messageCollection, 'add remove', updateLastMessage);
+            this.listenTo(this.model, 'newmessage', updateLastMessage);
+
             extension.windows.onClosed(this.stopListening.bind(this));
             this.timeStampView = new Whisper.TimestampView({brief: true});
             this.model.updateLastMessage();