Make rewind work on DBC

runtime/observatory/tests/service/rewind_optimized_out_test.dart

Index: runtime/observatory/tests/service/rewind_optimized_out_test.dart
diff --git a/runtime/observatory/tests/service/rewind_optimized_out_test.dart b/runtime/observatory/tests/service/rewind_optimized_out_test.dart
index 23b8c9a9a67015471d12df23ba8759f2b0c4ff8b..d6a246d939a72f2676c2a39e346414874b454f75 100644
--- a/runtime/observatory/tests/service/rewind_optimized_out_test.dart
+++ b/runtime/observatory/tests/service/rewind_optimized_out_test.dart
@@ -68,9 +68,10 @@ var tests = [
       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);
   },