code: private boolean verifyLastArgumentIsString(Node methodName, Node arg) {
      return verifyNotNull(methodName, arg)
          && verifyOfType(methodName, arg, Token.STRING)
          && verifyIsLast(methodName, arg);
    }
docs: Verifies that a method call has exactly one argument, and that it's a string literal. Reports a
  compile error if it doesn't.
  
  @return Whether the argument checked out okay