sync: Add DeviceInfo protobuf and supporting code

sync/internal_api/public/base_node.h

Index: sync/internal_api/public/base_node.h
diff --git a/sync/internal_api/public/base_node.h b/sync/internal_api/public/base_node.h
index d4ba99df3836c1819b5c518944d48f6d37f45c32..456e9921042d57629bcfafc6f68882e98bee958b 100644
--- a/sync/internal_api/public/base_node.h
+++ b/sync/internal_api/public/base_node.h
@@ -165,6 +165,10 @@ class BaseNode {
   // data.  Can only be called if GetModelType() == SESSIONS.
   const sync_pb::SessionSpecifics& GetSessionSpecifics() const;
 
+  // Getter specific to the DEVICE_INFO datatype.  Returns protobuf
+  // data.  Can only be called if GetModelType() == DEVICE_INFO.
+  const sync_pb::DeviceInfoSpecifics& GetDeviceInfoSpecifics() const;
+
   const sync_pb::EntitySpecifics& GetEntitySpecifics() const;
 
   // Returns the local external ID associated with the node.