anchor.diff:    void visitMapLiteral(MapLiteral node) {
       TypeArgumentList typeArguments = node.typeArguments;
   
  -    DartType mapDynamicType = _typeProvider.mapType
  -        .instantiate(<DartType>[_dynamicType, _dynamicType]);
  -
       // If we have type arguments, use them
       if (typeArguments != null) {
         DartType staticKeyType = _dynamicType;
  
positive.code:     var ts = _typeSystem as StrongTypeSystemImpl;
      ParameterizedType inferred = ts.inferGenericFunctionOrType(
          _typeProvider.mapType, parameters, elementTypes, contextType,
          downwards: downwards,
          errorReporter: _resolver.errorReporter,
          errorNode: node);
  
negative.code:               .instantiate(<DartType>[staticKeyType, staticValueType]));
        return;
      }
  
      DartType mapDynamicType = _typeProvider.mapType
          .instantiate(<DartType>[_dynamicType, _dynamicType]);
  
      // If we have no explicit type arguments, try to infer type arguments.
      ParameterizedType inferred = inferMapType(node);
  