Hello, I'm afraid that this is not possible because your Nexus 6P is designed to be charged with a 3A power charger (3 amps/hour) and the Huawei AP81 charger is a 5A because it is designed to power Huawei smartphones with this same characteristic (like my Huawei Mate 9 Pro) Moreover, the AP81 charger is equipped with a microprocessor that detects which type of device is connected and the power circuit adapts to it. In conclusion, your "assembly" would be possible but the fast charge functionality might not work, due to the lack of a device from another manufacturer like your Nexus.
I hope to have enlightened you as well as possible with my explanation. Ah the labyrinths of computing, ... Sincerely.