include type parameters on generic sync/async functions

lib/src/compiler/code_generator.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:collection' show HashMap, HashSet;
 import 'dart:math' show min, max;
 
 import 'package:analyzer/analyzer.dart' hide ConstantEvaluator;
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart' show Token, TokenType;
@@ skipping 1863 matching lines @@
       FormalParameterList parameters, FunctionBody body) {
     FunctionType type = element.type;
 
     // sync*, async, async*
     if (element.isAsynchronous || element.isGenerator) {
       return new JS.Fun(
           visitFormalParameterList(parameters, destructure: false),
           new JS.Block([
             _emitGeneratorFunctionBody(element, parameters, body).toReturn()
           ]),
+          typeParams: _emitTypeFormals(type.typeFormals),
           returnType: emitTypeRef(type.returnType));
     }
 
     // normal function (sync)
     return new JS.Fun(visitFormalParameterList(parameters), _visit(body),
         typeParams: _emitTypeFormals(type.typeFormals),
         returnType: emitTypeRef(type.returnType));
   }
 
   JS.Expression _emitGeneratorFunctionBody(ExecutableElement element,
@@ skipping 2290 matching lines @@
 }
 
 bool isLibraryPrefix(Expression node) =>
     node is SimpleIdentifier && node.staticElement is PrefixElement;
 
 LibraryElement _getLibrary(AnalysisContext c, String uri) =>
     c.computeLibraryElement(c.sourceFactory.forUri(uri));
 
 bool _isDartRuntime(LibraryElement l) =>
     l.isInSdk && l.source.uri.toString() == 'dart:_runtime';