Add a new BitBuffer class to webrtc base.

Provides a read-only interface for reading byte and bit-sized data from
an underlying buffer in network/big-endian order. Also provides a method
for reading exponential golomb encoded values, which will be useful in
H.264 packet parsing (separate CL).

BUG=
R=pthatcher@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/49719004

Cr-Original-Commit-Position: refs/heads/master@{#9046}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: bbf7c864ad7b9c6b643ece24967cab77c87ad26c
6 files changed