The comment in base64.h implies that base::Base64Encode() can return false, but
this cannot happen in practice. Fix the comment.

The implementation of Base64Encode() attempts to check for the return value
MODP_B64_ERROR as a failure, but modp_b64_encode() cannot return this
value. Remove the check.

Remove unneeded integer cast.

Change the return type to void.

BUG=323357
TEST=base_unittests, compile all
TBR=jochen@chromium.org,miket@chromium.org,joi@chromium.org,akalin@chromium.org,sergeyu@chromium.org

Review URL: https://codereview.chromium.org/86913002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239759 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239759