Roll Observatory packages and add a roll script

packages/observe/lib/src/list_diff.dart

 // Copyright (c) 2013, 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.
 
 library observe.src.list_diff;
 
 import 'dart:math' as math;
 import 'dart:collection' show UnmodifiableListView;
 import 'change_record.dart' show ChangeRecord;
 
@@ skipping 372 matching lines @@
       continue;
     }
 
     splices.addAll(calcSplices(list, splice.index,
         splice.index + splice.addedCount, splice._removed, 0,
         splice.removed.length));
   }
 
   return splices;
 }