Generate StylePropertyShorthand from an .in file.

This will automatically generate the boiler plate code to map longhands
with shorthands and the other way around.

Review URL: https://chromiumcodereview.appspot.com/19773010

git-svn-id: svn://svn.chromium.org/blink/trunk@154596 bbb929c8-8fbe-4397-9dbb-9b2b20218538