net: add GlobalSign to Twitter CDN pins.

BUG=329961
R=palmer@chromium.org

Review URL: https://codereview.chromium.org/119403002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243302 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243302