Lay some foundation for our new pending state controller

AsyncDisplayKit/Private/ASPendingStateController.h

@@ -0,0 +1,45 @@
+//
+//  ASPendingStateController.h
+//  AsyncDisplayKit
+//
+//  Created by Adlai Holler on 1/7/16.
+//  Copyright © 2016 Facebook. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+
+@class ASDisplayNode;
+
+NS_ASSUME_NONNULL_BEGIN
+
+/**
+ A singleton that is responsible for applying changes to
+ UIView/CALayer properties of display nodes when they
+ have been set on background threads.
+ 
+ This controller will enqueue run-loop events to flush changes
+ but if you need 
+ */
+@interface ASPendingStateController : NSObject
+
++ (ASPendingStateController *)sharedInstance;
+
+@property (nonatomic, readonly) BOOL hasChanges;
+
+/**
+ Flush all pending states for nodes now. Any UIView/CALayer properties
+ that have been set in the background will be applied to their
+ corresponding views/layers before this method returns.
+ 
+ You must call this method on the main thread.
+ */
+- (void)flush;
+
+/**
+ Register this node as having pending state that needs
+ */
+- (void)registerNode:(ASDisplayNode *)node;
+
+@end
+
+NS_ASSUME_NONNULL_END