Fix strong mode warnings.

test/priority_queue_test.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.
 
 /// Tests priority queue implementations utilities.
 
 import "package:test/test.dart";
 
-import "package:collection/priority_queue.dart";
+import "package:collection/src/priority_queue.dart";
 
 void main() {
   testDefault();
   testInt(() => new HeapPriorityQueue<int>());
   testCustom((comparator) => new HeapPriorityQueue<C>(comparator));
 }
 
 void testDefault() {
   test('new PriorityQueue() returns a HeapPriorityQueue', () {
     expect(new PriorityQueue<int>(),
@@ skipping 146 matching lines @@
 int compareNeg(C c1, C c2) => c2.value - c1.value;
 
 class C implements Comparable {
   final int value;
   const C(this.value);
   int get hashCode => value;
   bool operator==(Object other) => other is C && value == other.value;
   int compareTo(C other) => value - other.value;
   String toString() => "C($value)";
 }