sync: Add DeviceInfo protobuf and supporting code

sync/internal_api/public/write_node.h

Index: sync/internal_api/public/write_node.h
diff --git a/sync/internal_api/public/write_node.h b/sync/internal_api/public/write_node.h
index 1993cdbfb8d230644c626a05eb28541d30683a36..a48f8a13fadd663c9f4ef62019d2506594d2d4b5 100644
--- a/sync/internal_api/public/write_node.h
+++ b/sync/internal_api/public/write_node.h
@@ -164,6 +164,10 @@ class WriteNode : public BaseNode {
   // Should only be called if GetModelType() == SESSIONS.
   void SetSessionSpecifics(const sync_pb::SessionSpecifics& specifics);
 
+  // Set the device info specifics.
+  // Should only be called if GetModelType() == DEVICE_INFO.
+  void SetDeviceInfoSpecifics(const sync_pb::DeviceInfoSpecifics& specifics);
+
   // Implementation of BaseNode's abstract virtual accessors.
   virtual const syncable::Entry* GetEntry() const OVERRIDE;