renderEncryptionPassphraseDialog_() {
    var passphraseDialog = new dialogs.Generic(
        chrome.i18n.getMessage('promptEncryptionPassphraseMessage'),
        goog.bind(
            function(passphrase) {
              goog.dispose(passphraseDialog);
              if (passphrase.length > 0) {
                this.renderEncryptionPassphraseConfirmDialog_(passphrase);
              }
            },
            this),
        dialogs.InputType.SECURE_TEXT, '',
        chrome.i18n.getMessage('actionEnterPassphrase'),
        chrome.i18n.getMessage('actionCancelPgpAction'));
    this.renderDialog(passphraseDialog);
  }
Renders the UI elements needed for requesting a passphrase for
symmetrically encrypting the current message.
@private