This doesn't belong here.

`ThreadUI.setMessageBody()` and `ThreadUI.fillMMS` should be consolidated into a single function defined in compose.js: `Compose.fromMessage(message)` (this matches the design of `Compose.fromDraft(draft)` and makes the code easier to follow and likely less bug prone).

```js

fromMessage: function(message) {
  this.clear();

  if (message.type === 'mms') {
    if (message.subject) {
      Compose.subject.content = message.subject;
      Compose.subject.show();
    }
    SMIL.parse(message, function(elements) {
      elements.forEach(function(element) {
        if (element.blob) {
          var attachment = new Attachment(element.blob, {
            name: element.name,
            isDraft: true
          });
          Compose.append(attachment);
        }
        if (element.text) {
          Compose.append(element.text);
        }
      });
    });
  } else {
    this.append(message.body);
  }

  this.focus();
}
```

For reference see: https://github.com/rwaldron/gaia/blob/5f46aede8a6aaa3d2cefe35bd508aedb65c2a325/apps/sms/js/compose.js#L328-L363