Adds InternalNode#freeze() API

Summary:
Litho needs a new API which is called immediately before yoga begins layout calculations so that the InternalNode gets the opportunity to finalise itself; i.e. perform the last mutations and in effect avoid any more mutations to the hierarchy.

See D26373731 where the mutations from `Layout#collectResults` is moved back into the InternalNode.

Changelog: [Internal]  Adds new API to YogaNodeJNIBase

Reviewed By: SidharthGuglani

Differential Revision: D26373730

fbshipit-source-id: 471346d3444986ada91e86c95f5f9fb98bcd2fa6

java/com/facebook/yoga/YogaNodeJNIBase.java

@@ -197,12 +197,17 @@ public abstract class YogaNodeJNIBase extends YogaNode implements Cloneable {
     long[] nativePointers = null;
     YogaNodeJNIBase[] nodes = null;
 
+    freeze();
+
     ArrayList<YogaNodeJNIBase> n = new ArrayList<>();
     n.add(this);
     for (int i = 0; i < n.size(); ++i) {
       List<YogaNodeJNIBase> children = n.get(i).mChildren;
       if (children != null) {
-        n.addAll(children);
+        for (YogaNodeJNIBase child : children) {
+          child.freeze();
+          n.add(child);
+        }
       }
     }
 
@@ -215,6 +220,13 @@ public abstract class YogaNodeJNIBase extends YogaNode implements Cloneable {
     YogaNative.jni_YGNodeCalculateLayoutJNI(mNativePointer, width, height, nativePointers, nodes);
   }
 
+  private void freeze() {
+    Object data = getData();
+    if (data instanceof Inputs) {
+      ((Inputs) data).freeze();
+    }
+  }
+
   public void dirty() {
     YogaNative.jni_YGNodeMarkDirtyJNI(mNativePointer);
   }