Support serialization of the compiler backbone.

tests/compiler/dart2js/analyze_unused_dart2js_test.dart

 // Copyright (c) 2013, 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 analyze_unused_dart2js;
 
 import 'package:async_helper/async_helper.dart';
 
 import 'package:compiler/src/dart2jslib.dart';
 import 'package:compiler/src/filenames.dart';
@@ skipping 20 matching lines @@
       "The class 'Base", "The method 'error", "The method 'visit"],
 
   // Uncalled type predicate.  Keep while related predicates are used.
   "lib/src/ssa/nodes.dart": const [
       "The method 'isArray' is never called"],
 
   // Method in abstract class. Currently only instantiated trough tests.
   "lib/src/constants/expressions.dart": const [
       "The method 'readFromEnvironment' is never called"],
 
+  // Serialization code is only used in test.
+  "lib/src/serialization/": const [
+      "is never"],
+
   // Nested functions are currently kept alive in the IR.
   "lib/src/tree_ir/": const [
     "accept", "FunctionExpression", "CreateFunction"
   ],
 
   "lib/src/cps_ir/": const [
     "accept", "CreateFunction",
   ],
 
   "/lib/src/dart_backend/backend_ast_to_frontend_ast.dart": const [
@@ skipping 27 matching lines @@
     } else if (member.isTypedef) {
       if (member.isResolved) {
         compiler.reportHint(member, MessageKind.GENERIC,
             {'text': "Helper typedef in production code '$member'."});
       }
     }
   }
   compiler.libraryLoader.lookupLibrary(helperUri).forEachLocalMember(checkLive);
   return handler.checkResults();
 }