Free memory used in tests to enable use of valgrind

Summary: Its very usefull to be able to run valgrind on the tests and benchmarks. We were previously not freeing test memory so valgrind output was very messy.

Reviewed By: javache

Differential Revision: D3937493

fbshipit-source-id: 23c6970d7769b081575d39de583ba954fc65a397

gentest/gentest.js

@@ -93,6 +93,7 @@ function printTest(LTRContainer, RTLContainer, genericContainer) {
       return curr + '\n  ' + prev;
     }));
 
+    lines.push('\n  CSSNodeFreeRecursive(root);')
     lines.push('}');
     lines.push('');
   }