[ChromeDriver] W3C compliant unknown capability handling

Per W3C spec, unrecognized capabilities should trigger invalid argument
error, instead of being silently ignored.

Bug: chromedriver:1997
Change-Id: I84b2a888ad97d709737368b9394c8efdd475bf3a
Reviewed-on: https://chromium-review.googlesource.com/c/1325562
Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
Commit-Queue: John Chen <johnchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606733}
7 files changed