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 aba388541281ed5f89ee3e75b7554c031752de93..024a4f46b2e0e55514daff6a22c5b0576172eaa3 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
 
@@ -37,6 +38,11 @@ CC_EXPORT bool operator!=(const LayerSelectionBound& lhs,
 
 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_