code: private Node createUnstubCall(Node functionNode, int stubId) {
      return astFactory
          .createCall(
              // We can't look up the type of the stub creating method, because we add its
              // definition after type checking.
              astFactory.createNameWithUnknownType(UNSTUB_METHOD_NAME),
              astFactory.createNumber(stubId),
              functionNode)
          .useSourceInfoIfMissingFromForTree(functionNode);
    }
docs: Returns a new Node to be used as the stub definition for a method.
  
  @param functionNode actual function definition to be attached. Must be detached now.
  @param stubId ID to use for stubbing and unstubbing
  @return a Node that looks like <code>JSCompiler_unstubMethod(0, function() {})</code>