Generate code for static IDL attributes

BUG=163226
TEST=fast/notifications/notifications-permission-expected.txt
R=haraken@chromium.org

Review URL: https://chromiumcodereview.appspot.com/24354003

git-svn-id: svn://svn.chromium.org/blink/trunk@158225 bbb929c8-8fbe-4397-9dbb-9b2b20218538