Make Java YogaNode cloneable

Summary:
This diff exposes the YogaNode clone operation to JNI in order to be able to clone Java YogaNode objects.

The clone method performs a shallow copy of the java YogaNode.

I made YogaNode to implement Cloneable, I know that this might not be a good idea but in this case it simplifies the cloning mechanism. I am open to suggestions.

IMPORTANT NOTES:
- The current implementation IS NOT making a deep copy of the mData instance variable.
- The mParent Java instance variable will reference the parent of the original Java YogaNode, is that ok sebmarkbage?

Reviewed By: priteshrnandgaonkar

Differential Revision: D6935971

fbshipit-source-id: a2008f1eb849b5074585b48699b7de56d5ac90d4

java/com/facebook/yoga/YogaNode.java

@@ -16,7 +16,7 @@ import java.util.List;
 import javax.annotation.Nullable;
 
 @DoNotStrip
-public class YogaNode {
+public class YogaNode implements Cloneable {
 
   static {
     SoLoader.loadLibrary("yoga");
@@ -31,7 +31,7 @@ public class YogaNode {
   private List<YogaNode> mChildren;
   private YogaMeasureFunction mMeasureFunction;
   private YogaBaselineFunction mBaselineFunction;
-  private final long mNativePointer;
+  private long mNativePointer;
   private Object mData;
 
   /* Those flags needs be in sync with YGJNI.cpp */
@@ -160,6 +160,18 @@ public class YogaNode {
     jni_YGNodeInsertChild(mNativePointer, child.mNativePointer, i);
   }
 
+  private native long jni_YGNodeClone(long nativePointer, Object newNode);
+
+  @Override
+  public YogaNode clone() throws CloneNotSupportedException {
+    YogaNode clonedYogaNode = (YogaNode) super.clone();
+    long clonedNativePointer = jni_YGNodeClone(mNativePointer, clonedYogaNode);
+    clonedYogaNode.mNativePointer = clonedNativePointer;
+    clonedYogaNode.mChildren =
+        mChildren != null ? (List<YogaNode>) ((ArrayList) mChildren).clone() : null;
+    return clonedYogaNode;
+  }
+
   private native void jni_YGNodeRemoveChild(long nativePointer, long childPointer);
   public YogaNode removeChildAt(int i) {