Fetch libexif 0.6.21 to include the security fixes.
BUG=none
TEST=none
Review URL: https://chromiumcodereview.appspot.com/
10792004
git-svn-id: http://src.chromium.org/svn/trunk/deps/third_party/libexif@146817
4ff67af0-8c30-449e-8e8b-
ad334ec8d88c
Add libexif to deps/third_party.
BUG=none
TEST=none
Review URL: https://chromiumcodereview.appspot.com/
10535156
git-svn-id: http://src.chromium.org/svn/trunk/deps/third_party/libexif@141967
4ff67af0-8c30-449e-8e8b-
ad334ec8d88c