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 3b07c5dfd367897ce1e7b7524846c66c1908072a..4121ea5956b75d14dbf8d3e4b0d0082311e1dfa0 100644
--- a/cc/layers/picture_layer_impl.h
+++ b/cc/layers/picture_layer_impl.h
@@ -27,6 +27,14 @@ class CC_EXPORT PictureLayerImpl
     : public LayerImpl,
       NON_EXPORTED_BASE(public PictureLayerTilingClient) {
  public:
+  struct CC_EXPORT Pair {
+    Pair();

[reveman, 2014/07/19 00:45:50]

I think adding a ctor that takes 2 layers as input will clean up
LayerTreeHostImpl::GetPictureLayerImplPairs a bit.

[vmpstr, 2014/07/20 01:15:04]

Done.

+    ~Pair();
+
+    PictureLayerImpl* active;
+    PictureLayerImpl* pending;
+  };
+
   class CC_EXPORT LayerRasterTileIterator {
    public:
     LayerRasterTileIterator();