[ChromeDriver] W3C-compliant process capabilities

Re-implement processing of capabilities based on W3C spec.

spec: https://www.w3.org/TR/webdriver/#processing-capabilities

Bug: chromedriver:1997
Change-Id: I3304c54ba886b2319b178dad38a09713e349da25
Reviewed-on: https://chromium-review.googlesource.com/c/1260506
Commit-Queue: John Chen <johnchen@chromium.org>
Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596689}
5 files changed