These methods allow us to move some buffers out of a pickle with minimum
copying. It's useful when the IPC deserialized type uses BufferList to
store data and we want to take the buffers from IPC directly.
Borrowing is not suitable to use for IPC to hand out data because we
often want to store the data somewhere for processing after IPC has
released the underlying buffers.
MozReview-Commit-ID: F1K2ZMkACqq
Kan-Ru Chen
Bill McCloskey