Expose logging capablities in Yoga header

Summary: Exposes a bool in the config which will help log the yoga hierarchy. Also added a test case

Reviewed By: IanChilds

Differential Revision: D9560577

fbshipit-source-id: ef4998107ed51ea374853bab7cbe09e3232caa0c

yoga/YGConfig.h

@@ -1,10 +1,10 @@
-/**
- * Copyright (c) 2014-present, Facebook, Inc.
+/*
+ *  Copyright (c) 2014-present, Facebook, Inc.
+ *
+ *  This source code is licensed under the MIT license found in the LICENSE
+ *  file in the root directory of this source tree.
  *
- * This source code is licensed under the MIT license found in the
- * LICENSE file in the root directory of this source tree.
  */
-
 #pragma once
 #include "Yoga-internal.h"
 #include "Yoga.h"
@@ -18,6 +18,7 @@ struct YGConfig {
   YGLogger logger;
   YGCloneNodeFunc cloneNodeCallback;
   void* context;
+  bool printTree;
 
   YGConfig(YGLogger logger);
 };