Fix --compile_all flag (--compile-all is wrong)

runtime/observatory/tests/service/native_metrics_test.dart

 // Copyright (c) 2015, 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=--compile-all --error_on_bad_type --error_on_bad_override
+// VMOptions=--compile_all --error_on_bad_type --error_on_bad_override
 
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
 
 import 'dart:profiler';
 
 void script() {
   var counter = new Counter('a.b.c', 'description');
   Metrics.register(counter);
@@ skipping 31 matching lines @@
       expect(e.message,
              "_getIsolateMetric: invalid 'metricId' "
              "parameter: metrics/native/doesnotexist");
     }
     expect(caughtException, isTrue);
   },
 
 ];
 
 main(args) => runIsolateTests(args, tests, testeeBefore: script);