code: function beginSearch(prefix, initialString) {
          function createDialog() {
              _curDialog = new QuickNavigateDialog();
              _curDialog.showDialog(prefix, initialString);
          }
  
          if (_curDialog) {
              if (_curDialog.isOpen) {
                  // Just start a search using the existing dialog.
                  _curDialog.setSearchFieldValue(prefix, initialString);
              } else {
                  // The dialog is already closing. Wait till it's done closing,
                  // then open a new dialog. (Calling close() again returns the
                  // promise for the deferred that was already kicked off when it
                  // started closing.)
                  _curDialog.close().done(createDialog);
              }
          } else {
              createDialog();
          }
      }
docs: Opens the Quick Open bar prepopulated with the given prefix (to select a mode) and optionally
  with the given query text too. Updates text field contents if Quick Open already open.
  @param {?string} prefix
  @param {?string} initialString