Copy Mark Seaborn from the Native Client authors file to the Chromium authors

file. This makes the Native Client authors file a subset of the Chromium one
so that we can update the copyright notices of the code we recently moved into
the Chrome repo to be "Copyright the Chromium Authors."

TEST=none
BUG=none
Review URL: http://codereview.chromium.org/7770001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@98499 0039d316-1c4b-4281-b951-d872f2087c98

AUTHORS

@@ -119,3 +119,4 @@ Luke Zarko <lukezarko@gmail.com>
 Felix H. Dahlke <fhd@ubercode.de>
 Ali Vathi <ali.akbar@gmail.com>
 Mathias Bynens <mathias@qiwi.be>
+Mark Seaborn <mrs@mythic-beasts.com>