Fix more strong mode errors in analyzer

pkg/analyzer/lib/src/task/driver.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.driver;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/src/context/cache.dart';
@@ skipping 579 matching lines @@
   /**
    * The work order that this item is part of, may be `null`.
    */
   WorkOrder workOrder;
 
   /**
    * An iterator used to iterate over the descriptors of the inputs to the task,
    * or `null` if all of the inputs have been collected and the task can be
    * created.
    */
-  TaskInputBuilder builder;
+  TopLevelTaskInputBuilder builder;
 
   /**
    * The [TargetedResult]s outputs of this task depends on.
    */
   final HashSet<TargetedResult> inputTargetedResults =
       new HashSet<TargetedResult>();
 
   /**
    * The inputs to the task that have been computed.
    */
@@ skipping 249 matching lines @@
   final TaskManager taskManager;
 
   _WorkOrderDependencyWalker(this.taskManager, WorkItem startingNode)
       : super(startingNode);
 
   @override
   WorkItem getNextInput(WorkItem node, List<WorkItem> skipInputs) {
     return node.gatherInputs(taskManager, skipInputs);
   }
 }