DRY up registration event callbacks

This was just a special case of the extension.on/trigger interface.

js/background.js

@@ -38,6 +38,6 @@
         }
     };
 
-    textsecure.registration.addListener(init);
+    extension.on('registration_done', init);
     init();
 })();

js/chromium.js

@@ -38,7 +38,12 @@
         chrome.runtime.sendMessage(null, { name: name, data: object });
     };
 
-    window.extension.onMessage = function (name, callback) {
+    window.extension.on = function (name, callback) {
+        // this causes every listener to fire on every message.
+        // if we eventually end up with lots of listeners (lol)
+        // might be worth making a map of 'name' -> [callbacks, ...]
+        // so we can fire a single listener that calls only the necessary
+        // calllbacks for that message name
         chrome.runtime.onMessage.addListener(function(e) {
             if (e.name === name) {
                 callback(e.data);
@@ -50,20 +55,12 @@
     window.textsecure.registration = {
         done: function () {
             localStorage.setItem("chromiumRegistrationDone", "");
-            chrome.runtime.sendMessage('registration_done');
+            extension.trigger('registration_done');
             window.location = '/index.html';
         },
 
         isDone: function () {
             return localStorage.getItem("chromiumRegistrationDone") !== null;
         },
-
-        addListener: function (callback) {
-            chrome.runtime.onMessage.addListener(function(message) {
-                if (message === 'registration_done') {
-                    callback();
-                }
-            });
-        }
     };
 }());

js/views/inbox_view.js

@@ -42,7 +42,7 @@
                 }
             }.bind(this));
 
-            extension.onMessage('message', function(message) {
+            extension.on('message', function(message) {
                 this.conversations.fetch({id: message.conversationId}).then(function() {
                     this.conversations.get(message.conversationId).fetchMessages();
                 }.bind(this));