anchor.diff:      if (parent is ir.Procedure && parent.kind == ir.ProcedureKind.Factory) {
         _addClassTypeVariablesIfNeeded(parent);
       }
  +    _potentiallyAddFunctionParameterTypeChecks(functionNode);
   
       if (closedWorld.nativeData.isNativeMember(targetElement)) {
         nativeEmitter.nativeMethods.add(targetElement);
  
positive.code:     closeFunction();
    }
  
    /// Builds a SSA graph for FunctionNodes of external methods.
    void buildExternalFunctionNode(ir.FunctionNode functionNode) {
      assert(functionNode.body == null);
  
negative.code:   void buildConstructorBody(ir.Constructor constructor) {
      openFunction(constructor.function);
      _addClassTypeVariablesIfNeeded(constructor);
      _potentiallyAddFunctionParameterTypeChecks(constructor.function);
      constructor.function.body.accept(this);
      closeFunction();
    }
  