GitLab

Refactored InitSessionHelper for better test coverage. Extracted
ConfigureHeadlessSession function, and added unit tests.

Bug: chromedriver:3102
Change-Id: I6ac964c923924d8b6205a87710e2468c40acf5fd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1792796Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Tricia Crichton <triciac@chromium.org>
Cr-Commit-Position: refs/heads/master@{#694966}