Introduce debug events for Microtask queue.

test/mjsunit/es6/debug-promises-uncaught-uncaught.js

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Flags: --expose-debug-as debug
 
 // Test debug events when we only listen to uncaught exceptions and
 // there is a catch handler for the exception thrown in a Promise.
 // We expect an Exception debug event with a promise to be triggered.
 
 Debug = debug.Debug;
 
 var log = [];
 var step = 0;
 
 var p = new Promise(function(resolve, reject) {
   log.push("resolve");
   resolve();
 });
 
 var q = p.chain(
   function() {
     log.push("throw");
     throw new Error("uncaught");  // event
   });
 
 function listener(event, exec_state, event_data, data) {
+  if (event == Debug.DebugEvent.AsyncTaskEvent) return;
   try {
     // Ignore exceptions during startup in stress runs.
     if (step >= 1) return;
     assertEquals(["resolve", "end main", "throw"], log);
     if (event == Debug.DebugEvent.Exception) {
       assertEquals(0, step);
       assertEquals("uncaught", event_data.exception().message);
       assertTrue(event_data.promise() instanceof Promise);
       assertEquals(q, event_data.promise());
       assertTrue(event_data.uncaught());
       // Assert that the debug event is triggered at the throw site.
       assertTrue(exec_state.frame(0).sourceLineText().indexOf("// event") > 0);
       step++;
     }
   } catch (e) {
     // Signal a failure with exit code 1.  This is necessary since the
     // debugger swallows exceptions and we expect the chained function
     // and this listener to be executed after the main script is finished.
     print("Unexpected exception: " + e + "\n" + e.stack);
     quit(1);
   }
 }
 
 Debug.setBreakOnUncaughtException();
 Debug.setListener(listener);
 
 log.push("end main");