createHandle_(address, descriptor) {
    if (address[0] === this.worldId_) {
      const existing = this.idToHandle_.get(address[1]);
      if (existing)
        return existing;
    }

    const localAddress = [this.worldId_, descriptor.name + '#' + (++this.lastHandleId_)];
    return new Handle(localAddress, address, descriptor, this);
  }
Unwraps descriptor and creates a local world handle that will be associated
with the primary handle at given address.

@param {!Address} address Address of the primary wrapper.
@param {!Descriptor} address Address of the primary wrapper.
@return {!Handle}