Add support for (de)serializing HeadsUpDisplayLayer

cc/layers/heads_up_display_layer.cc

Index: cc/layers/heads_up_display_layer.cc
diff --git a/cc/layers/heads_up_display_layer.cc b/cc/layers/heads_up_display_layer.cc
index 388c2ad2473e520d29e3da6c294af0ca63389c79..158186f3c6ee98df1a399b5ffba0c23920147686 100644
--- a/cc/layers/heads_up_display_layer.cc
+++ b/cc/layers/heads_up_display_layer.cc
@@ -8,6 +8,7 @@
 
 #include "base/trace_event/trace_event.h"
 #include "cc/layers/heads_up_display_layer_impl.h"
+#include "cc/proto/layer.pb.h"
 #include "cc/trees/layer_tree_host.h"
 
 namespace cc {
@@ -61,4 +62,9 @@ scoped_ptr<LayerImpl> HeadsUpDisplayLayer::CreateLayerImpl(
   return HeadsUpDisplayLayerImpl::Create(tree_impl, layer_id_);
 }
 
+void HeadsUpDisplayLayer::SetTypeForProtoSerialization(
+    proto::LayerNode* proto) const {
+  proto->set_type(proto::LayerType::HEADS_UP_DISPLAY_LAYER);
+}
+
 }  // namespace cc