Use dartfmt on Observatory code

runtime/observatory/lib/src/repositories/megamorphiccache.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 MegamorphicCacheRepository extends M.MegamorphicCacheRepository {
-  Future<M.MegamorphicCache> get(M.IsolateRef i, String id) async{
+  Future<M.MegamorphicCache> get(M.IsolateRef i, String id) async {
     S.Isolate isolate = i as S.Isolate;
     assert(isolate != null);
     return (await isolate.getObject(id)) as S.MegamorphicCache;
   }
 }