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

runtime/observatory/tests/service/echo_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.
-// VMOptions=--compile-all --error_on_bad_type --error_on_bad_override
+// VMOptions=--compile_all --error_on_bad_type --error_on_bad_override
 
 import 'dart:async';
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
 
 var tests = [
 
 (Isolate isolate) =>
   isolate.vm.invokeRpc('_echo', { 'text': 'hello'}).then((result) {
@@ skipping 13 matching lines @@
   var subscription;
   subscription = stream.listen((ServiceEvent event) {
     assert(event.kind == '_Echo');
     expect(event.data.lengthInBytes, equals(3));
     expect(event.data.getUint8(0), equals(0));
     expect(event.data.getUint8(1), equals(128));
     expect(event.data.getUint8(2), equals(255));
     subscription.cancel();
     completer.complete();
   });
-  
+
   await isolate.invokeRpc('_triggerEchoEvent', { 'text': 'hello' });
   await completer.future;
 },
 
 ];
 
 main(args) => runIsolateTests(args, tests);