Fix ineffective --disable-gpu-driver-bug-workarounds

It was hidden to the user since chrome://gpu was not showing
any workarounds, but they were still applied in the gpu process.

Also add a gpu test that sets
--disable-gpu-driver-bug-workarounds --use_gpu_driver_workaround_for_testing
and verifies that the only active workaround is USE_TESTING_GPU_DRIVER_WORKAROUND
in both browser and gpu processes.

BUG=359367

R=kbr@chromium.org, zmo@chromium.org

TEST=./content/test/gpu/run_gpu_test.py gpu_process --show-stdout --browser=exact --extra-browser-args="--no-sandbox" --browser-executable=./out/build/chrome
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Committed: https://crrev.com/d18006d595e7b6bf070f9ab9777d353ac8457755
Committed: https://crrev.com/7eee382917c50ad10a487ef1c1402adc8c84e9fd
Committed: https://crrev.com/87c144ab365dacd92f2bb7720628e3397a44c2d6
Review-Url: https://codereview.chromium.org/2195743005
Cr-Original-Original-Original-Commit-Position: refs/heads/master@{#409197}
Cr-Original-Original-Commit-Position: refs/heads/master@{#412685}
Cr-Original-Commit-Position: refs/heads/master@{#412989}
Cr-Commit-Position: refs/heads/master@{#413411}
3 files changed