Add PhantomRef based YogaNode subclass

Summary: Adds a subclass of `YogaNodeJNIBase` that uses `PhantomReference` for deallocating native memory rather than `Object#finalize()`. This should help making garbage collection more efficient.

Reviewed By: amir-shalem

Differential Revision: D16182667

fbshipit-source-id: d310fdb6af184168c43462b24f5e18ab5d0d7ad0

java/com/facebook/yoga/YogaNodeJNIFinalizer.java

@@ -0,0 +1,34 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the LICENSE
+ * file in the root directory of this source tree.
+ */
+package com.facebook.yoga;
+
+public class YogaNodeJNIFinalizer extends YogaNodeJNIBase {
+  public YogaNodeJNIFinalizer() {
+    super();
+  }
+
+  public YogaNodeJNIFinalizer(YogaConfig config) {
+    super(config);
+  }
+
+  @Override
+  protected void finalize() throws Throwable {
+    try {
+      freeNatives();
+    } finally {
+      super.finalize();
+    }
+   }
+
+  public void freeNatives() {
+    if (mNativePointer != 0) {
+      long nativePointer = mNativePointer;
+      mNativePointer = 0;
+      YogaNative.jni_YGNodeFree(nativePointer);
+    }
+  }
+}