Implement enum types in VM

runtime/lib/core_patch.dart

Index: runtime/lib/core_patch.dart
===================================================================
--- runtime/lib/core_patch.dart	(revision 41810)
+++ runtime/lib/core_patch.dart	(working copy)
@@ -10,3 +10,14 @@
 void  _asyncCatchHelper(catchFunction, continuation) {
   catchFunction((e) => continuation(null, e));
 }
+
+// The members of this class are cloned and added to each class that
+// represents an enum type.
+class _EnumHelper {
+  // Declare the list of enum value names private. When this field is
+  // cloned into a user-defined enum class, the field will be inaccessible
+  // because of the library-specific name suffix. The toString() function
+  // below can access it because it uses the same name suffix.
+  static const List<String> _enum_names = null;
+  String toString() => _enum_names[index];
+}