Fix bug in DoubleLinkedQueue where removing from empty queue throws.

tests/corelib/queue_test.dart

Index: tests/corelib/queue_test.dart
diff --git a/tests/corelib/queue_test.dart b/tests/corelib/queue_test.dart
index 3cf139ff8808d5307bced4f636b9e2d576990374..e590dce63142ad74463610464bb39e4891e45705 100644
--- a/tests/corelib/queue_test.dart
+++ b/tests/corelib/queue_test.dart
@@ -237,6 +237,13 @@ abstract class QueueTest {
     Expect.listEquals(
         [6, 8, 9, 1, 2, 4, 5, 6, 8, 9, 10, 1, 2, 4, 5, 6, 8, 9, 10, 1, 2, 4, 5],
         queue.toList());
+
+    // Regression test: http://dartbug.com/16270
+    // These should all do nothing, and should not throw.
+    Queue emptyQueue = newQueue();
+    emptyQueue.remove(0);
+    emptyQueue.removeWhere((x) => null);
+    emptyQueue.retainWhere((x) => null);
   }
 
   void testLarge() {