Add a PRESUBMIT check for 'printf'.

As we all know, printf debugging is best debugging. But debug code
should probably be removed before asking people to review a patch.
Otherwise you're bound to look a bit silly.

Review URL: https://chromiumcodereview.appspot.com/22366003

git-svn-id: svn://svn.chromium.org/blink/trunk@155687 bbb929c8-8fbe-4397-9dbb-9b2b20218538