[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/ASDisplayNode+Beta.h

@@ -10,6 +10,7 @@
 
 #import "ASDisplayNode.h"
 #import "ASLayoutRangeType.h"
+#import "ASTraceEvent.h"
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -18,6 +19,20 @@ void ASPerformBlockOnMainThread(void (^block)());
 void ASPerformBlockOnBackgroundThread(void (^block)()); // DISPATCH_QUEUE_PRIORITY_DEFAULT
 ASDISPLAYNODE_EXTERN_C_END
 
+#ifndef ASDISPLAYNODE_EVENTLOG_CAPACITY
+#define ASDISPLAYNODE_EVENTLOG_CAPACITY 20
+#endif
+
+#ifndef ASDISPLAYNODE_EVENTLOG_ENABLE
+#define ASDISPLAYNODE_EVENTLOG_ENABLE DEBUG
+#endif
+
+#if ASDISPLAYNODE_EVENTLOG_ENABLE
+#define ASDisplayNodeLogEvent(node, ...) [node _logEventWithBacktrace:[NSThread callStackSymbols] format:__VA_ARGS__]
+#else
+#define ASDisplayNodeLogEvent(node, ...)
+#endif
+
 /**
  * Bitmask to indicate what performance measurements the cell should record.
  */
@@ -110,6 +125,20 @@ extern NSString *const ASDisplayNodeLayoutGenerationNumberOfPassesKey;
  */
 + (void)setRangeModeForMemoryWarnings:(ASLayoutRangeMode)rangeMode;
 
+#if ASDISPLAYNODE_EVENTLOG_ENABLE
+
+/**
+ * The primitive event tracing method. You shouldn't call this. Use the ASDisplayNodeLogEvent macro instead.
+ */
+- (void)_logEventWithBacktrace:(NSArray<NSString *> *)backtrace format:(NSString *)format, ... NS_FORMAT_FUNCTION(2, 3);
+
+/**
+ * @abstract The most recent trace events for this node. Max count is ASDISPLAYNODE_EVENTLOG_CAPACITY.
+ */
+@property (readonly, copy) NSArray *eventLog;
+
+#endif
+
 @end
 
 NS_ASSUME_NONNULL_END