Sync LayoutTests/resources/ with LayoutTests/external/wpt/resources/

Roll in the most recent version of:
testharness.js, testdriver.js, idlharness.js.

(webidl2.js has not changed in wpt)

Bug: 892613
Change-Id: I38208e6f796ebd2428716ed53219d5c21a188a90
Reviewed-on: https://chromium-review.googlesource.com/c/1262716
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Commit-Queue: Philip Jägenstedt <foolip@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597863}
3 files changed