cc: Change TileManager iterators to be queues.

cc/layers/picture_layer_impl.cc

Index: cc/layers/picture_layer_impl.cc
diff --git a/cc/layers/picture_layer_impl.cc b/cc/layers/picture_layer_impl.cc
index 4a7e0c0b0b66ae5bdf20743b65c0f51c69824c0d..4ff86e002671d969ef73fa7d4adefd9269504dbf 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -46,6 +46,17 @@ const int kMinDimensionsForAnalysis = 256;
 
 namespace cc {
 
+PictureLayerImpl::Pair::Pair() : active(NULL), pending(NULL) {
+}
+
+PictureLayerImpl::Pair::Pair(PictureLayerImpl* active_layer,
+                             PictureLayerImpl* pending_layer)
+    : active(active_layer), pending(pending_layer) {
+}
+
+PictureLayerImpl::Pair::~Pair() {
+}
+
 PictureLayerImpl::PictureLayerImpl(LayerTreeImpl* tree_impl, int id)
     : LayerImpl(tree_impl, id),
       twin_layer_(NULL),