Add the ability to attach data to a java CSSNode

Summary: The C version already has this ability via the same name 'context'. This can be used to attach arbitrary data about your view hierarchy to a CSSNode. Previously this could only be done in java via subclassing CSSNode.

Reviewed By: lucasr

Differential Revision: D3662065

fbshipit-source-id: 560a768092f17381e99b349d08bd4a8b365541be

java/com/facebook/csslayout/CSSNodeJNI.java

@@ -33,6 +33,7 @@ public class CSSNodeJNI implements CSSNodeAPI<CSSNodeJNI> {
   private List<CSSNodeJNI> mChildren;
   private MeasureFunction mMeasureFunction;
   private int mNativePointer;
+  private Object mData;
 
   private void assertNativeInstance() {
     if (mNativePointer == 0) {
@@ -718,4 +719,14 @@ public class CSSNodeJNI implements CSSNodeAPI<CSSNodeJNI> {
   public boolean valuesEqual(float f1, float f2) {
     return FloatUtil.floatsEqual(f1, f2);
   }
+
+  @Override
+  public void setData(Object data) {
+    mData = data;
+  }
+
+  @Override
+  public Object getData() {
+    return mData;
+  }
 }