Add chrome://flags#enable-sxg-subresource-prefetching

Bug: 935267
Change-Id: Ibec8974f52a703ac3930517ce3a9de0bfb13f94f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1619582
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Kunihiko Sakamoto <ksakamoto@chromium.org>
Commit-Queue: Tsuyoshi Horo <horo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661319}
5 files changed