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This is a reland of be44dc6b

Original change's description:
> [ChromeDriver] Making CloseWindow W3C Compliant
> 
> Making CloseWindow W3C compliant by returning the result of
> GetWindowHandles. Modified testCloseWindow in run_py_tests.py
> to test this conformance.
> 
> Bug: chromedriver:1990
> Change-Id: I2e90e9e9ca16559ea3678846a7d605b402b4d431
> Reviewed-on: https://chromium-review.googlesource.com/1115813
> Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
> Reviewed-by: John Chen <johnchen@chromium.org>
> Commit-Queue: Cole Winstanley <cwinstanley@google.com>
> Cr-Commit-Position: refs/heads/master@{#571334}

Bug: chromedriver:1990
Change-Id: Iac9b60f09aeb697151077410dbcb408dbba420c2
Reviewed-on: https://chromium-review.googlesource.com/1120696Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Cole Winstanley <cwinstanley@google.com>
Cr-Commit-Position: refs/heads/master@{#571639}