Introduce debug events for promises.

src/debug.h

Index: src/debug.h
diff --git a/src/debug.h b/src/debug.h
index b672940c0f9ef58738c3d2dfeb8bfc91267b9526..8c1fe268bf976487d5132d0d016aac432797204a 100644
--- a/src/debug.h
+++ b/src/debug.h
@@ -376,6 +376,7 @@ class Debug {
   void OnAfterCompile(Handle<Script> script,
                       AfterCompileFlags after_compile_flags);
   void OnScriptCollected(int id);
+  void OnPromiseEvent(Handle<JSObject> data);
 
   // API facing.
   void SetEventListener(Handle<Object> callback, Handle<Object> data);
@@ -550,6 +551,8 @@ class Debug {
   MUST_USE_RESULT MaybeHandle<Object> MakeCompileEvent(
       Handle<Script> script, bool before);
   MUST_USE_RESULT MaybeHandle<Object> MakeScriptCollectedEvent(int id);
+  MUST_USE_RESULT MaybeHandle<Object> MakePromiseEvent(
+      Handle<JSObject> promise_event);
 
   // Mirror cache handling.
   void ClearMirrorCache();