Here we add slightly improved detection for the goma flag.
The detection of goma in autoninja does not work for the use_goma flag
when it does not simply appear at the beginning of the line.

Below are examples of multi-arg lines we now support:
is_debug=false use_goma=true is_official_build=false
use_goma=false# use_goma=true This comment is ignored


Also adding linux nice process launch feature to improve the user
experience when running a large build. This feature is disabled by
default like other autoninja features.



R=brucedawson@chromium.org

Change-Id: I8a04e7480c5e8d37d57fb71143c6066d46abb004
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2479683
Commit-Queue: Peter McNeeley <petermcneeley@chromium.org>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>