Revert 239759 "The comment in base64.h implies that base::Base64..."

> 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

TBR=ricea@chromium.org

Review URL: https://codereview.chromium.org/101113004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239921 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239921