[Feature Request]: want to get parent promise from PromiseHookInit through async

[Feature Request]: want to get parent promise from PromiseHookInit through async_hooks

Version:
v8.0.0-nightly20170527f84666f923
Platform:
Subsystem:

Chrome V8 PromiseHook init hook's signature is PromiseHookInit(promise,parentPromise),
current async_hooks seems not support to get the parentPromise, is that possible to get the
the parentPromise from async_hooks init callback?

Thank you very much!