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* Eliminate references to Windows
* Specify the binary to run
* Document GN args

Bug: none
Test: markdown preview
Change-Id: I29b3179b4b74289a35e53cf2cd2ff5658ef7df6e
Reviewed-on: https://chromium-review.googlesource.com/884321Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#531729}