Use ninja by default on Linux for build-webkit --chromium, bot edition
https://bugs.webkit.org/show_bug.cgi?id=104434

Reviewed by Eric Seidel.

r139557 changed update-webkit to pick ninja by default on linux, but
the bots run update-webkit-chromium directly so they didn't see this.
Move the default for ninja into update-webkit-chromium so that it's
picked up by the bots, and let update-webkit forward non-default
options to there.

This way, the default is in one place only and both developers (who
usually use update-webkit which then shells out to
updat-webkit-chromium) and bots (which use update-webkit-chromium
directly) see the same behavior.

* Scripts/update-webkit:
* Scripts/update-webkit-chromium:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@139559 268f45cc-cd09-0410-ab3c-d52691b4dbfc