Revert of cc: Change TileManager iterators to be queues.

cc/layers/picture_layer_impl.h

Index: cc/layers/picture_layer_impl.h
diff --git a/cc/layers/picture_layer_impl.h b/cc/layers/picture_layer_impl.h
index 7af27f977f60eb48af89e6948a2f081a35b8d968..3b07c5dfd367897ce1e7b7524846c66c1908072a 100644
--- a/cc/layers/picture_layer_impl.h
+++ b/cc/layers/picture_layer_impl.h
@@ -27,15 +27,6 @@
     : public LayerImpl,
       NON_EXPORTED_BASE(public PictureLayerTilingClient) {
  public:
-  struct CC_EXPORT Pair {
-    Pair();
-    Pair(PictureLayerImpl* active_layer, PictureLayerImpl* pending_layer);
-    ~Pair();
-
-    PictureLayerImpl* active;
-    PictureLayerImpl* pending;
-  };
-
   class CC_EXPORT LayerRasterTileIterator {
    public:
     LayerRasterTileIterator();