Finish @nex3's strong-mode fixes in package:collection and test it in Travis

lib/src/priority_queue.dart

 // Copyright (c) 2014, 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.
 
 import "dart:collection";
 
 /// A priority queue is a priority based work-list of elements.
 ///
 /// The queue allows adding elements, and removing them again in priority order.
 abstract class PriorityQueue<E> {
@@ skipping 103 matching lines @@
 ///   an expected O(n*log(n)) time.
 class HeapPriorityQueue<E> implements PriorityQueue<E> {
   /// Initial capacity of a queue when created, or when added to after a
   /// [clear].
   ///
   /// Number can be any positive value. Picking a size that gives a whole
   /// number of "tree levels" in the heap is only done for aesthetic reasons.
   static const int _INITIAL_CAPACITY = 7;
 
   /// The comparison being used to compare the priority of elements.
-  final Comparator comparison;
+  final Comparator<E> comparison;
 
   /// List implementation of a heap.
   List<E> _queue = new List<E>(_INITIAL_CAPACITY);
 
   /// Number of elements in queue.
   ///
   /// The heap is implemented in the first [_length] entries of [_queue].
   int _length = 0;
 
   /// Create a new priority queue.
@@ skipping 210 matching lines @@
   ///
   /// Called when the list is full.
   void _grow() {
     int newCapacity = _queue.length * 2 + 1;
     if (newCapacity < _INITIAL_CAPACITY) newCapacity = _INITIAL_CAPACITY;
     List<E> newQueue = new List<E>(newCapacity);
     newQueue.setRange(0, _length, _queue);
     _queue = newQueue;
   }
 }