Introduce more debug events for promises.

test/mjsunit/es6/debug-promises-new-event.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
 
 Debug = debug.Debug;
 
 var exception = null;
 var new_promise;
 
 function listener(event, exec_state, event_data, data) {
-  if (event != Debug.DebugEvent.PromiseEvent) return;
+  if (!(event_data instanceof debug.NewPromiseEvent)) return;
   try {
     assertTrue(event_data.resolver().isFunction());
     assertEquals(resolver, event_data.resolver().value());
     assertTrue(event_data.resolver().resolved());
     assertEquals("resolver", event_data.resolver().name());
     assertTrue(event_data.resolver().source().indexOf("Token") > 0);
 
     assertTrue(event_data.promise().isPromise());
     new_promise = event_data.promise().value();
     assertEquals("pending", event_data.promise().status());
   } catch (e) {
     print(e + e.stack)
     exception = e;
   }
 }
 
 Debug.setListener(listener);
 
 function resolver(resolve, reject) {
   resolve();  // Token
 }
 
 var p = new Promise(resolver);
 assertEquals(new_promise, p);
 
 assertNull(exception);
 Debug.setListener(null);