Add support for (de)serializing LayerSelection.

cc/input/layer_selection_bound.h

Index: cc/input/layer_selection_bound.h
diff --git a/cc/input/layer_selection_bound.h b/cc/input/layer_selection_bound.h
index fa1739930625f06b26da6776d7dd7ef9063b633c..333d1eff569873930f256d2a9f3352351293e4de 100644
--- a/cc/input/layer_selection_bound.h
+++ b/cc/input/layer_selection_bound.h
@@ -13,6 +13,7 @@
 namespace cc {
 
 namespace proto {
+class LayerSelection;
 class LayerSelectionBound;
 }  // namespace proto
 
@@ -35,6 +36,11 @@ struct CC_EXPORT LayerSelectionBound {
 
 typedef Selection<LayerSelectionBound> LayerSelection;
 
+CC_EXPORT void LayerSelectionToProtobuf(const LayerSelection& selection,
+                                        proto::LayerSelection* proto);
+CC_EXPORT void LayerSelectionFromProtobuf(LayerSelection* selection,
+                                          const proto::LayerSelection& proto);
+
 }  // namespace cc
 
 #endif  // CC_INPUT_LAYER_SELECTION_BOUND_H_