Pulling in https://android-review.googlesource.com/#/c/186482/1

Fix memory leak in HWUI

std::unique_ptr::release just releases the ownership of the
managed object. To delete the object, std::unique_ptr::reset
function should be called.

Bug: 26116596
Change-Id: If65f74085b1fc2be3a9fffc433326e0bcdb40ff3