GitLab

1. Check path and session id from request and accept WebSocket connection
if valid
2. Only allow one connection per session
3. If connection closed, session id can be reused to establish connection
4. Add tests for accepting and rejecting connection
5. Reverted some changes in https://chromium-review.googlesource.com/c/chromium/src/+/1730860

Public design doc:
https://docs.google.com/document/d/1zixFBPtgFFwhc5pT1IfneFoW6yZfpvYdQRsNN4tbghk/

Previous CL chain(I, II and III):
I. https://chromium-review.googlesource.com/c/chromium/src/+/2382299
II. https://chromium-review.googlesource.com/c/chromium/src/+/2389053
II. https://chromium-review.googlesource.com/c/chromium/src/+/2391903

Bug: chromedriver:3588
Change-Id: Idbdd2c17e2b04f23c78c5a36f1f5585e94819d5b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2406661
Commit-Queue: Shengfa Lin <shengfa@google.com>
Reviewed-by: Yoichi Osato <yoichio@chromium.org>
Reviewed-by: John Chen <johnchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#810314}