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
diff --git a/base/base_tests.gyp b/base/base_tests.gyp
index 3a9b164..d9e560e 100644
--- a/base/base_tests.gyp
+++ b/base/base_tests.gyp
@@ -53,6 +53,7 @@
           'base64_unittest.cc',
           'basictypes_unittest.cc',
           'bind_unittest.cc',
+          'bitbuffer_unittest.cc',
           'buffer_unittest.cc',
           'bytebuffer_unittest.cc',
           'byteorder_unittest.cc',