[api] add API for Promise status and result.

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index b57a9ca9acbc914163d0b7be90d6ae2e4d47205c..e4d3d0b77bb719d6c7cd32ba1c5261d27be6af2a 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -3699,6 +3699,8 @@ class V8_EXPORT Function : public Object {
  */
 class V8_EXPORT Promise : public Object {
  public:
+  enum PromiseStatus { kPending, kFulfilled, kRejected };

[jochen (gone - plz use gerrit), 2016/12/20 07:49:52]

why not an enum class?

also, please add a comment explaining what the values mean

[Yang, 2016/12/20 11:38:27]

enum class requires static_cast all over the place because we use this enum as
an integer value when storing as a smi.

+
   class V8_EXPORT Resolver : public Object {
    public:
     /**
@@ -3755,6 +3757,10 @@ class V8_EXPORT Promise : public Object {
    */
   bool HasHandler();
 
+  MaybeLocal<Value> Result();

[jochen (gone - plz use gerrit), 2016/12/20 07:49:52]

please also add a comment to document this API (and Status() below)

[Yang, 2016/12/20 11:38:27]

Done.

+
+  PromiseStatus Status();
+
   V8_INLINE static Promise* Cast(Value* obj);
 
  private: