Fix TestSimpleChromeWorkflow.

Goma was enabled for build_package. However, as its sideeffect,
TestSimpleChromeWorkflow's GN argument starts to include
use_goma = true, even if --nogoma option is set, unexpectedly.

This CL fixes it, by setting use_goma = false, if --nogoma is set,
even if original GN_ARGS contains "use_goma = true".

BUG=chromium:712297
TEST=Ran cros_chrome_sdk_unittest.

Change-Id: I7d3c44661442533fbd2c9204350ca88b75daee19
Reviewed-on: https://chromium-review.googlesource.com/479971
Tested-by: Hidehiko Abe <hidehiko@chromium.org>
Trybot-Ready: Hidehiko Abe <hidehiko@chromium.org>
Reviewed-by: Owen Lin <owenlin@chromium.org>
Reviewed-by: Ilja H. Friedel <ihf@chromium.org>
Commit-Queue: Owen Lin <owenlin@chromium.org>
2 files changed