Add WebFeature::kOffMainThreadFetch

Bug: 443374
Change-Id: Idae54521a5c7ff87eef74aa5c556f1dae48febb9
Reviewed-on: https://chromium-review.googlesource.com/602837
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Commit-Queue: Tsuyoshi Horo <horo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#492301}
6 files changed