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/YogaNode.java

@@ -10,6 +10,14 @@
 import javax.annotation.Nullable;
 
 public abstract class YogaNode {
+
+  /** The interface the {@link #getData()} object can optionally implement. */
+  public interface Inputs {
+
+    /** Requests the data object to disable mutations of its inputs. */
+    void freeze();
+  }
+
   public abstract void reset();
 
   public abstract int getChildCount();
@@ -25,12 +33,10 @@ public abstract class YogaNode {
   public abstract YogaNode removeChildAt(int i);
 
   /**
-   * @returns the {@link YogaNode} that owns this {@link YogaNode}.
-   * The owner is used to identify the YogaTree that a {@link YogaNode} belongs
-   * to.
-   * This method will return the parent of the {@link YogaNode} when the
-   * {@link YogaNode} only belongs to one YogaTree or null when the
-   * {@link YogaNode} is shared between two or more YogaTrees.
+   * @returns the {@link YogaNode} that owns this {@link YogaNode}. The owner is used to identify
+   *     the YogaTree that a {@link YogaNode} belongs to. This method will return the parent of the
+   *     {@link YogaNode} when the {@link YogaNode} only belongs to one YogaTree or null when the
+   *     {@link YogaNode} is shared between two or more YogaTrees.
    */
   @Nullable
   public abstract YogaNode getOwner();

java/com/facebook/yoga/YogaNodeJNIBase.java

@@ -197,12 +197,17 @@ public void calculateLayout(float width, float height) {
     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 void calculateLayout(float width, float height) {
     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);
   }