enableLookingGlass_() {
    if (!this.isGmail_()) {
      return;
    }

    this.api_.getCurrentMessage(goog.bind(function(messageElemSelector) {
      try {
        var messageElem = document.querySelector(messageElemSelector);
        if (!messageElem || Boolean(messageElem.lookingGlass)) {
          return;
        }
      } catch (e) {  // document.querySelector might throw.
        return;
      }
      var selectionBody =
          e2e.openpgp.asciiArmor.extractPgpBlock(messageElem.innerText);
      var action = utils.text.getPgpAction(selectionBody);
      if (action == constants.Actions.DECRYPT_VERIFY) {
        var glass = new ui.GlassWrapper(messageElem);
        this.registerDisposable(glass);
        glass.installGlass();
      }
    }, this), goog.bind(this.errorHandler_, this, goog.nullFunction));
  }
Enables the looking glass for the current message in Gmail.
@private