[ASDisplayNode] Add Event Tracing to Help Debugging (#2243)

* Add some simple event logging for ASDisplayNode

Improve the tracing

* Add header to copy files phase

* Make event header public

AsyncDisplayKit/Private/ASDisplayNodeInternal.h

@@ -121,7 +121,10 @@ FOUNDATION_EXPORT NSString * const ASRenderingEngineDidDisplayNodesScheduledBefo
 
   UIEdgeInsets _hitTestSlop;
   NSMutableArray *_subnodes;
-  
+  NSMutableArray<ASTraceEvent *> *_eventLog;
+  // The index of the most recent log entry. -1 until first entry.
+  NSInteger _eventLogHead;
+
   // Main thread only
   BOOL _automaticallyManagesSubnodes;
   _ASTransitionContext *_pendingLayoutTransitionContext;