Add support for (de)serializing HeadsUpDisplayLayer

cc/layers/heads_up_display_layer.h

Index: cc/layers/heads_up_display_layer.h
diff --git a/cc/layers/heads_up_display_layer.h b/cc/layers/heads_up_display_layer.h
index 5ffa31aa0c9e2cbcb40bdee9cab91b19c01ea1de..554d33ee7c7952e5749d662dc99ed6034bbb305a 100644
--- a/cc/layers/heads_up_display_layer.h
+++ b/cc/layers/heads_up_display_layer.h
@@ -14,6 +14,10 @@
 
 namespace cc {
 
+namespace proto {
+class LayerNode;
+}  // namespace proto
+
 class CC_EXPORT HeadsUpDisplayLayer : public Layer {
  public:
   static scoped_refptr<HeadsUpDisplayLayer> Create(
@@ -24,6 +28,8 @@ class CC_EXPORT HeadsUpDisplayLayer : public Layer {
 
   scoped_ptr<LayerImpl> CreateLayerImpl(LayerTreeImpl* tree_impl) override;
 
+  void SetTypeForProtoSerialization(proto::LayerNode* proto) const override;
+
  protected:
   explicit HeadsUpDisplayLayer(const LayerSettings& settings);
   bool HasDrawableContent() const override;