Introduce debug events for Microtask queue.

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index 888f665d21c8d8ab126a7d0ff9703d534094d5aa..29dcbfafafa0aa72634cdb25bd6364a65cd772a3 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -5535,6 +5535,15 @@ RUNTIME_FUNCTION(Runtime_DebugPromiseEvent) {
 }
 
 
+RUNTIME_FUNCTION(Runtime_DebugAsyncTaskEvent) {
+  ASSERT(args.length() == 1);
+  HandleScope scope(isolate);
+  CONVERT_ARG_HANDLE_CHECKED(JSObject, data, 0);
+  isolate->debug()->OnAsyncTaskEvent(data);
+  return isolate->heap()->undefined_value();
+}
+
+
 RUNTIME_FUNCTION(Runtime_DeleteProperty) {
   HandleScope scope(isolate);
   ASSERT(args.length() == 3);