Repurpose "HexEncoding" for internal users.

Frameworks callers either roll their own or use an internal apache
class. Given that apache is going away, we need to provide them with
an alternative.

bug: 18027885
Change-Id: Iec01cba9f3d2027828457c0b450eac0dd08fcaf6
Merge "Repurpose "HexEncoding" for internal users."