Reland "[ChromeDriver] Add ChromeDriver tests to Commit Queue"

This is a reland of aa7860c74a88b62a1cc2e0505777d4caf6a84dcb,
with the change to enable the ChromeDriver tests on release bot only.
The original commit was reverted due to flakiness of the tests on debug
build. The reason for the flakiness is debug build of Chrome takes a
long time to start, usually between 20 to 40 seconds. The timeout for
the test is 30 seconds, thus it can either succeed or fail depending
on whether Chrome started quick enough or not.

While it is possible to increase the timeout, spending over 30 seconds
per test appears to be too much overhead in the long run. Also, the
purpose of running these tests is to catch incompatibilities that can
develop between Chrome and ChromeDriver, and running these tests on
release builds should suffice for that purpose.

Original change's description:
> [ChromeDriver] Add ChromeDriver tests to Commit Queue
>
> This is the initial check-in of the feature to add ChromeDriver tests
> to commit queue. It includes the following:
>
> * A new test target chromedriver_py_tests, to encapsulate dependencies
>   needed to run the Python-based ChromeDriver tests. This target is
>   currently enabled on Linux only. Other platforms will be added later.
>
> * Only a single test case is enabled. Enabling additional test cases
>   will be done later.
>
> Bug: 793370
> Change-Id: I5a6f0568d2e78724a4fe53e84c3a480d770c3e47
> Reviewed-on: https://chromium-review.googlesource.com/874816
> Commit-Queue: John Chen <[email protected]>
> Reviewed-by: John Budorick <[email protected]>
> Reviewed-by: Daniel Cheng <[email protected]>
> Reviewed-by: Caleb Rouleau <[email protected]>
> Cr-Commit-Position: refs/heads/master@{#531234}

Bug: 793370
Change-Id: Ic8873c326dfcd676552083d6f90aba29cc046e67
Reviewed-on: https://chromium-review.googlesource.com/885082
Reviewed-by: Caleb Rouleau <[email protected]>
Reviewed-by: Daniel Cheng <[email protected]>
Reviewed-by: John Budorick <[email protected]>
Commit-Queue: John Chen <[email protected]>
Cr-Commit-Position: refs/heads/master@{#532252}
8 files changed