Fix header guard and remove AURA_EXPORT

Header guard was wrong and AURA_EXPORT shouldn't be in .cc.

BUG=none
TEST=none
R=ben@chromium.org
TBR=ben@chromium.org

Review URL: https://codereview.chromium.org/118503004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241867 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241867