Revert "Remove Registry from registerMetadataConstant" and "Serialize metadata"

tests/compiler/dart2js/serialization/test_helper.dart

 // Copyright (c) 2016, 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.serialization_test_helper;
 
 import 'dart:collection';
 import 'package:compiler/src/common/resolution.dart';
 import 'package:compiler/src/constants/expressions.dart';
 import 'package:compiler/src/dart_types.dart';
@@ skipping 418 matching lines @@
 
   testResolutionImpactEquivalence(impact1, impact2, const CheckStrategy());
 }
 
 void checkSets(
     Iterable set1,
     Iterable set2,
     String messagePrefix,
     bool sameElement(a, b),
     {bool failOnUnfound: true,
-    bool failOnExtra: true,
     bool verbose: false,
     void onSameElement(a, b)}) {
   List<List> common = <List>[];
   List unfound = [];
   Set remaining = computeSetDifference(
       set1, set2, common, unfound,
       sameElement: sameElement,
       checkElements: onSameElement);
   StringBuffer sb = new StringBuffer();
   sb.write("$messagePrefix:");
   if (verbose) {
     sb.write("\n Common:\n  ${common.join('\n  ')}");
   }
   if (unfound.isNotEmpty || verbose) {
     sb.write("\n Unfound:\n  ${unfound.join('\n  ')}");
   }
   if (remaining.isNotEmpty || verbose) {
     sb.write("\n Extra: \n  ${remaining.join('\n  ')}");
   }
   String message = sb.toString();
   if (unfound.isNotEmpty || remaining.isNotEmpty) {
 
-    if ((failOnUnfound && unfound.isNotEmpty) ||
-        (failOnExtra && remaining.isNotEmpty)) {
+    if (failOnUnfound || remaining.isNotEmpty) {
       Expect.fail(message);
     } else {
       print(message);
     }
   } else if (verbose) {
     print(message);
   }
 }
 
 String defaultToString(obj) => '$obj';
@@ skipping 72 matching lines @@
         (mismatch.isNotEmpty && failOnMismatch) ||
         remaining.isNotEmpty) {
       Expect.fail(message);
     } else {
       print(message);
     }
   } else if (verbose) {
     print(message);
   }
 }