Delay dropping root views until the drop views step of StateBuilder.

Summary: Make UIOperation public so that custom implementations can expose instances of it.

Reviewed By: ahmedre

Differential Revision: D3618197

fbshipit-source-id: 89f764818cc2e8e94cf9678814e56e7074eb9067

ReactAndroid/src/main/java/com/facebook/react/uimanager/UIViewOperationQueue.java

@@ -48,7 +48,7 @@ public class UIViewOperationQueue {
   /**
    * A mutation or animation operation on the view hierarchy.
    */
-  protected interface UIOperation {
+  public interface UIOperation {
 
     void execute();
   }