dart2js: Use frequency of occurence to sort metadata indices.

pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart

 // Copyright (c) 2014, 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.ir_nodes_sexpr;
 
 import '../constants/values.dart';
 import '../util/util.dart';
 import 'cps_ir_nodes.dart';
 
@@ skipping 385 matching lines @@
   }
 
   String visitType(TypeConstantValue constant, _) {
     return '(Type "${constant.representedType}")';
   }
 
   String visitInterceptor(InterceptorConstantValue constant, _) {
     return _failWith(constant);
   }
 
-  String visitDummy(DummyConstantValue constant, _) {
+  String visitSynthetic(SyntheticConstantValue constant, _) {
     return _failWith(constant);
   }
 
   String visitDeferred(DeferredConstantValue constant, _) {
     return _failWith(constant);
   }
 }
 
 class _Namer {
   final Map<Node, String> _names = <Node, String>{};
@@ skipping 28 matching lines @@
   void setReturnContinuation(Continuation node) {
     assert(!_names.containsKey(node) || _names[node] == 'return');
     _names[node] = 'return';
   }
 
   String getName(Node node) {
     if (!_names.containsKey(node)) return 'MISSING_NAME';
     return _names[node];
   }
 }