[ChromeDriver] Implement Release Actions for keys

Add "input cancel list" to the session state, as required by W3C spec,
and use it to implement Release Actions command for keyboard actions.
Fixes WPT test webdriver/tests/release_actions/sequence.py, subtest
test_release_char_sequence_sends_keyup_events_in_reverse.

Bug: chromedriver:1897
Change-Id: I95893b08ad59d366806964b53ef2cbdbc117063f
Reviewed-on: https://chromium-review.googlesource.com/c/1435683
Reviewed-by: Lan Wei <lanwei@chromium.org>
Commit-Queue: John Chen <johnchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#627735}
3 files changed