Don't double-escape in strings in the VM Service, and don't use \u0000 to determine the string lengt

runtime/bin/vmservice/observatory/test/contexts_test.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 inbound_references_test;
 
 import 'dart:async';
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
@@ skipping 54 matching lines @@
 
 (Isolate isolate) =>
   isolate.rootLib.load().then((Library lib) {
     ServiceMap field = lib.variables.singleWhere((v) => v.name == 'copyingBlock');
     return field['value'].load().then((Instance block) {
       expect(block.isClosure, isTrue);
       expect(block.closureCtxt.isContext, isTrue);
       expect(block.closureCtxt.length, equals(1));
       return block.closureCtxt.load().then((Context ctxt) {
         expect(ctxt.variables.single['value'].isString, isTrue);
-        expect(ctxt.variables.single['value'].valueAsString, equals('"I could be copied into the block"'));
+        expect(ctxt.variables.single['value'].valueAsString, equals('I could be copied into the block'));
         expect(block.closureCtxt.parentContext.isNull, isTrue);
       });
     });
   }),
 
 (Isolate isolate) =>
   isolate.rootLib.load().then((Library lib) {
     ServiceMap field = lib.variables.singleWhere((v) => v.name == 'fullBlock');
     return field['value'].load().then((Instance block) {
       expect(block.isClosure, isTrue);
@@ skipping 24 matching lines @@
           expect(outerCtxt.variables.single['value'].valueAsString, equals('421'));
           expect(outerCtxt.parentContext.isNull, isTrue);
         });
       });
     });
   }),
 
 ];
 
 main(args) => runIsolateTests(args, tests, testeeBefore: script);