Small refactor of attachment views

Bind the sub-view to some data when we initialize it, rather than
passing it in on render. That means the image view click handler will
only ever open the blob we bound it to, even if its src attr changes for
some reason, which should never happen, but if it does, it's nice to
guard against opening arbitrary urls found in the dom.

// FREEBIE

js/views/attachment_view.js

@@ -6,6 +6,9 @@
 
   var ImageView = Backbone.View.extend({
       tagName: 'img',
+      initialize: function(dataUrl) {
+          this.dataUrl = dataUrl;
+      },
       events: {
           'load': 'update',
           'click': 'open'
@@ -14,16 +17,18 @@
         this.$el.trigger('update');
       },
       open: function () {
-        window.open(this.$el.attr('src'), '_blank');
+        window.open(this.dataUrl, '_blank');
       },
-      render: function(dataUrl) {
-          this.$el.attr('src', dataUrl);
+      render: function() {
+          this.$el.attr('src', this.dataUrl);
           return this;
       }
   });
 
   var MediaView = Backbone.View.extend({
-      initialize: function() {
+      initialize: function(dataUrl, contentType) {
+          this.dataUrl = dataUrl;
+          this.contentType = contentType;
           this.$el.attr('controls', '');
       },
       events: {
@@ -32,10 +37,10 @@
       update: function() {
         this.$el.trigger('update');
       },
-      render: function(dataUrl, contentType) {
+      render: function() {
           var $el = $('<source>');
-          $el.attr('src', dataUrl);
-          $el.attr('type', contentType);
+          $el.attr('src', this.dataUrl);
+          $el.attr('type', this.contentType);
           this.$el.append($el);
           return this;
       }
@@ -48,17 +53,18 @@
     tagName: 'span',
     className: 'attachment',
     render: function() {
-        var view;
+        var View;
         switch(this.model.contentType.split('/')[0]) {
-            case 'image': view = new ImageView(); break;
-            case 'audio': view = new AudioView(); break;
-            case 'video': view = new VideoView(); break;
+            case 'image': View = ImageView; break;
+            case 'audio': View = AudioView; break;
+            case 'video': View = VideoView; break;
             default:
                 throw 'Unsupported attachment type';
         }
-        view.$el.appendTo(this.$el);
         var blob = new Blob([this.model.data], {type: this.model.contentType});
-        view.render(window.URL.createObjectURL(blob), this.model.contentType);
+        var view = new View(window.URL.createObjectURL(blob), this.model.contentType);
+        view.$el.appendTo(this.$el);
+        view.render();
         return this;
     }
   });