1305205 - Stop using mozharness to run web platform tests

Status: NEW

(Testing :: web-platform-tests, defect)

Description

[Gregory Szorc [:gps]]

mozharness adds little value to web platform test running after bug 1286900 transitions WPT to run from a source checkout. Let's convert web platform tests to not run from mozharness.

Note that as long as we have buildbot, this will be difficult since buildbot is hard-coded to invoke a mozharness script. We may need to retain a very minimal mozharness script that essentially invokes `mach` (or whatever we'll use to launch the tests).

There's a bit of other work involved here, namely some build system infrastructure to set up a workspace with binaries, etc (the "download-and-extract" mozharness step). So this will likely morph into a tracking bug of sorts.