Implement @patch annotation for patch class members

runtime/lib/expando_patch.dart

Index: runtime/lib/expando_patch.dart
diff --git a/runtime/lib/expando_patch.dart b/runtime/lib/expando_patch.dart
index abdefabaa5df7e98d9545cf2e10466a878360ea9..ac5f706e934492908c266082852dfd0916baac53 100644
--- a/runtime/lib/expando_patch.dart
+++ b/runtime/lib/expando_patch.dart
@@ -3,14 +3,14 @@
 // BSD-style license that can be found in the LICENSE file.
 
 @patch class Expando<T> {
-  /* @patch */ Expando([String this.name])
+  @patch Expando([String this.name])
       : _data = new List(_minSize),
         _used = 0;
 
   static const _minSize = 8;
   static final _deletedEntry = new _WeakProperty(null, null);
 
-  /* @patch */ T operator[](Object object) {
+  @patch T operator[](Object object) {
     _checkType(object);
 
     var mask = _size - 1;
@@ -31,7 +31,7 @@
     return null;
   }
 
-  /* @patch */ void operator[]=(Object object, T value) {
+  @patch void operator[]=(Object object, T value) {
     _checkType(object);
 
     var mask = _size - 1;