Support `void` as generic argument.

pkg/compiler/lib/src/resolution/resolution.dart

 // Copyright (c) 2012, 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.
 
 library dart2js.resolution;
 
 import 'dart:collection' show Queue;
 
 import '../common.dart';
 import '../common/names.dart' show Identifiers;
@@ skipping 424 matching lines @@
       element.computeType(resolution);
 
       resolution.target.resolveNativeElement(element, registry.impactBuilder);
 
       return registry.impactBuilder;
     });
   }
 
   ResolutionDartType resolveTypeAnnotation(
       Element element, TypeAnnotation annotation) {
-    ResolutionDartType type = _resolveReturnType(element, annotation);
-    if (type.isVoid) {
-      reporter.reportErrorMessage(annotation, MessageKind.VOID_NOT_ALLOWED);
-    }
-    return type;
-  }
-
-  ResolutionDartType _resolveReturnType(
-      Element element, TypeAnnotation annotation) {
     if (annotation == null) return const ResolutionDynamicType();
     ResolutionDartType result =
         visitorFor(element).resolveTypeAnnotation(annotation);
     assert(invariant(annotation, result != null,
         message: "No type computed for $annotation."));
     if (result == null) {
       // TODO(karklose): warning.
       return const ResolutionDynamicType();
     }
     return result;
@@ skipping 675 matching lines @@
   TreeElements get treeElements {
     assert(invariant(this, _treeElements != null,
         message: "TreeElements have not been computed for $this."));
     return _treeElements;
   }
 
   void reuseElement() {
     _treeElements = null;
   }
 }