Add upstream code as of Chromium 279ad18

Copy the unchanged source from
https://chromium.googlesource.com/chromium/src/third_party/modp_b64. The latest
commit in Chromium was 279ad18 while the latest commit that touched
third_party/modp_b64 was e9705fd.

Added MODULE_LICENSE_BSD and NOTICE. The latter is identical to the existing
LICENSE file.

Bug: 22382625

Change-Id: I0e5d00abb84f087d20529aa1d2bf47b5cb4c75b5
11 files changed