Make rewind work on DBC

runtime/observatory/tests/service/rewind_optimized_out_test.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.
 // VMOptions=--error_on_bad_type --error_on_bad_override
 
 import 'dart:developer';
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'service_test_common.dart';
 import 'test_helper.dart';
@@ skipping 50 matching lines @@
 
     // Rewind the top stack frame.
     bool caughtException;
     try {
       result = await isolate.rewind(1);
       expect(false, isTrue, reason:'Unreachable');
     } on ServerRpcException catch(e) {
       caughtException = true;
       expect(e.code, equals(ServerRpcException.kCannotResume));
       expect(e.message,
-             'Cannot rewind to frame 1 due to conflicting compiler '
-             'optimizations. Run the vm with --no-prune-dead-locals to '
-             'disallow these optimizations. Next valid rewind frame is 4.');
+             startsWith('Cannot rewind to frame 1 due to conflicting compiler '
+                        'optimizations. Run the vm with --no-prune-dead-locals '
+                        'to disallow these optimizations. Next valid rewind '
+                        'frame is '));
     }
     expect(caughtException, isTrue);
   },
 ];
 
 
 main(args) => runIsolateTests(args, tests, testeeConcurrent: test,
                               extraArgs:
                               ['--trace-rewind',
                                '--prune-dead-locals',
                                '--enable-inlining-annotations',
                                '--no-background-compilation',
                                '--optimization-counter-threshold=10']);