It's not necessary to create HandleScope in v8 native binding functions,
because it's guarrenteed that the there is a upper HandleScope when the
native function is called. So unless we are urgent to free the handles,
not using HandleScope in native binding functions is a cleaner and safer
choice.
This API can monitor when the object is GCed by V8, this is required by
the RPC API since we want to make sure the remote object got destroied
when object in renderer is GCed.
