Shared workers should support --enable-experimental-webkit-features.

      Shared workers now share the same runtime feature code as renderers. And the
--enable-experimental-webkit-features flag is now passed to shared worker
processes.

BUG=248576

Review URL: https://chromiumcodereview.appspot.com/15967008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@205927 0039d316-1c4b-4281-b951-d872f2087c98