Roll Observatory packages and add a roll script

packages/analyzer/lib/src/task/manager.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.
 
 library analyzer.src.task.manager;
 
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/java_engine.dart';
 import 'package:analyzer/task/model.dart';
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   /**
    * Given a list of task [descriptors] that can be used to compute some
    * unspecified result, return the descriptor that will compute the result with
    * the least amount of work.
    */
   TaskDescriptor _findBestTask(List<TaskDescriptor> descriptors) {
     // TODO(brianwilkerson) Improve this implementation.
     return descriptors[0];
   }
 }