The flag removal would allow Skia to choose the better
AA algorithm for a better performance.

bug: chromium:817942 chromium:819185 chromium:817110

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I57f5b1c1ef88eb97172f8aa24be85b9f29c07b84
Reviewed-on: https://chromium-review.googlesource.com/976622Reviewed-by: Brandon Jones <bajones@chromium.org>
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Yuqian Li <liyuqian@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548199}