anchor.diff:        // _AsyncStarImpl has an example of the generated code.
         var gen = emitGeneratorFn((_) => [_asyncStarController]);
   
  -      var returnType = _getExpectedReturnType(function, coreTypes.streamClass);
  -      var asyncStarImpl = InterfaceType(asyncStarImplClass, [returnType]);
  +      var returnType = _getExpectedReturnType(function, _coreTypes.streamClass);
  +      var asyncStarImpl = InterfaceType(_asyncStarImplClass, [returnType]);
         return js.call('new #.new(#).stream', [_emitType(asyncStarImpl), gen]);
       }
   
  
positive.code:         ? ctorClass.rawType
          : InterfaceType(ctorClass, args.types);
  
      if (isFromEnvironmentInvocation(coreTypes, node)) {
        var value = _constants.evaluate(node);
        if (value is PrimitiveConstant) {
          return value.accept(this) as js_ast.Expression;
  
negative.code:     // TODO(markzipan): remove const check when we use front-end const eval
      if (!node.isConst) {
        var setType = visitInterfaceType(
            InterfaceType(_linkedHashSetClass, [node.typeArgument]));
        if (node.expressions.isEmpty) {
          return js.call('#.new()', [setType]);
        }
  