This code doesn't even get built unless you go out of your way to pass an
extension value at build time.
Change-Id: I92ffcdfb18505c96e5ef390c8954a54cee19967f
Reviewed-on: https://boringssl-review.googlesource.com/1063
Reviewed-by: Adam Langley <agl@google.com>
Initial fork from f2d678e6e89b6508147086610e985d4e8416e867 (1.0.2 beta).
(This change contains substantial changes from the original and
effectively starts a new history.)
