Add support for (de)serializing cc::Layer hierarchy.

cc/layers/layer.h

Index: cc/layers/layer.h
diff --git a/cc/layers/layer.h b/cc/layers/layer.h
index 2fec36364570707340f3d6bc57fb886b51e901ee..ebbfa66e370ca152778d8ef62bf6c7831f9fd743 100644
--- a/cc/layers/layer.h
+++ b/cc/layers/layer.h
@@ -25,6 +25,7 @@
 #include "cc/layers/paint_properties.h"
 #include "cc/layers/scroll_blocks_on.h"
 #include "cc/output/filter_operations.h"
+#include "cc/proto/layer.pb.h"
 #include "cc/trees/property_tree.h"
 #include "skia/ext/refptr.h"
 #include "third_party/skia/include/core/SkColor.h"
@@ -74,6 +75,7 @@ class CC_EXPORT Layer : public base::RefCounted<Layer>,
                         public LayerAnimationValueProvider {
  public:
   typedef LayerList LayerListType;
+  typedef base::hash_map<int, scoped_refptr<Layer>> LayerIdMap;
 
   enum LayerIdLabels {
     INVALID_ID = -1,
@@ -358,6 +360,23 @@ class CC_EXPORT Layer : public base::RefCounted<Layer>,
 
   virtual void PushPropertiesTo(LayerImpl* layer);
 
+  // Return the proto::LayerType that should be used for serialization of the
+  // current layer.
+  virtual proto::LayerType GetTypeForProtoSerialization() const;
+
+  // Recursively iterate over this layer and all children and write the
+  // hierarchical structure to the given LayerNode proto. In addition to the
+  // structure itself, the Layer id and type is also written to facilitate
+  // construction of the correct layer on the client.
+
+  void ToLayerNodeProto(proto::LayerNode* proto) const;

[vmpstr, 2015/10/26 17:51:45]

I meant like 

// comment
// comment
void function

// comment 
// comment
void function

:)

[nyquist, 2015/10/26 19:01:53]

Wow... I don't even... Sorry... :-/

+  // Recursively iterate over the given LayerNode proto and read the structure
+  // into this node and its children. The |layer_map| should be used to look
+  // for previously existing Layers, since they should be re-used between each
+  // hierarchy update.
+  virtual void FromLayerNodeProto(const proto::LayerNode& proto,

[vmpstr, 2015/10/26 17:51:45]

Can this also be non virtual?

[nyquist, 2015/10/26 19:01:53]

Doh... Yeah! Done.

+                                  const LayerIdMap& layer_map);
+
   LayerTreeHost* layer_tree_host() { return layer_tree_host_; }
   const LayerTreeHost* layer_tree_host() const { return layer_tree_host_; }