Use dartfmt on Observatory code

runtime/observatory/lib/src/models/objects/objectpool.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 models;
 
 abstract class ObjectPoolRef extends ObjectRef {
   int get length;
 }
 
 abstract class ObjectPool extends Object implements ObjectPoolRef {
   Iterable<ObjectPoolEntry> get entries;
 }
 
-enum ObjectPoolEntryKind {
-  object,
-  immediate,
-  nativeEntry
-}
+enum ObjectPoolEntryKind { object, immediate, nativeEntry }
 
 abstract class ObjectPoolEntry {
   int get offset;
   ObjectPoolEntryKind get kind;
   ObjectRef get asObject;
   int get asInteger;
 }