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

runtime/observatory/tests/service/dominator_tree_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';
 
 // small example from [Lenguaer & Tarjan 1979]
 class R { var x; var y; var z; }
 class A { var x; }
 class B { var x; var y; var z; }
 class C { var x; var y; }
@@ skipping 61 matching lines @@
   expect(node('F').dominator, equals(node('C')));
   expect(node('G').dominator, equals(node('C')));
   expect(node('J').dominator, equals(node('G')));
   expect(node('L').dominator, equals(node('D')));
 
   expect(node('R'), isNotNull);  // The field.
 },
 ];
 
 main(args) => runIsolateTests(args, tests, testeeBefore: buildGraph);