[Nit] Sorting run-webkit-tests options in alphabetical order.

run-webkit-tests --help prints a number of options which are unordered.
This makes it difficult to locate an option as the options are considerable in number.
Sorting them alphabetically eases the task of locating a particular option.

Review URL: https://codereview.chromium.org/452893002

git-svn-id: svn://svn.chromium.org/blink/trunk@181402 bbb929c8-8fbe-4397-9dbb-9b2b20218538