Move toString() to collection classes.

sdk/lib/collection/queue.dart

Index: sdk/lib/collection/queue.dart
diff --git a/sdk/lib/collection/queue.dart b/sdk/lib/collection/queue.dart
index 7bc65cab6fe5a63e7da2e3ae1881d748b6025f0d..0e1bb8ac9c2e5a69634d5a97a1d1cfe61ce23a95 100644
--- a/sdk/lib/collection/queue.dart
+++ b/sdk/lib/collection/queue.dart
@@ -301,9 +301,8 @@ class DoubleLinkedQueue<E> extends IterableBase<E> implements Queue<E> {
     return new _DoubleLinkedQueueIterator<E>(_sentinel);
   }
 
-  String toString() {
-    return ToString.iterableToString(this);
-  }
+  // TODO(zarah)  Remove this, and let it be inherited by IterableBase
+  String toString() => IterableMixinWorkaround.toStringIterable(this, '{', '}');
 }
 
 class _DoubleLinkedQueueIterator<E> implements Iterator<E> {
@@ -530,9 +529,8 @@ class ListQueue<E> extends IterableBase<E> implements Queue<E> {
     }
   }
 
-  String toString() {
-    return ToString.iterableToString(this);
-  }
+  // TODO(zarah)  Remove this, and let it be inherited by IterableBase
+  String toString() => IterableMixinWorkaround.toStringIterable(this, '{', '}');
 
   // Queue interface.