Use dartfmt on Observatory code

runtime/observatory/lib/src/repositories/strongly_reachable_instances.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
 
 part of repositories;
 
 class StronglyReachableInstancesRepository
     implements M.StronglyReachableInstancesRepository {
   Future<M.InstanceSet> get(M.IsolateRef i, M.ClassRef c,
-                                           {int limit: 100}) async {
+      {int limit: 100}) async {
     S.Isolate isolate = i as S.Isolate;
     S.Class cls = c as S.Class;
     assert(isolate != null);
     assert(cls != null);
     assert(limit != null);
-    return (await isolate.getInstances(cls, limit))
-        as S.InstanceSet;
+    return (await isolate.getInstances(cls, limit)) as S.InstanceSet;
   }
 }