anchor.diff:        : super(variable, promotedType);
   
     @override
  -  DartType _inferExpression(DartType typeContext, bool typeNeeded) {
  +  DartType _inferExpression(
  +      KernelTypeInferrer inferrer, DartType typeContext, bool typeNeeded) {
       // TODO(paulberry): implement.
       return typeNeeded ? const DynamicType() : null;
     }
  
positive.code: /// Concrete shadow object representing a null literal in kernel form.
  class KernelNullLiteral extends NullLiteral implements KernelExpression {
    @override
    DartType _inferExpression(DartType typeContext, bool typeNeeded) {
      // TODO(paulberry): implement.
      return typeNeeded ? const DynamicType() : null;
    }
  
negative.code:   KernelFunctionExpression(FunctionNode function) : super(function);
  
    @override
    DartType _inferExpression(
        KernelTypeInferrer inferrer, DartType typeContext, bool typeNeeded) {
      // TODO(paulberry): implement.
      return typeNeeded ? const DynamicType() : null;
    }
  