Support AppCache with off-main-thread-fetch

Bug: 443374
Change-Id: I8a20173a40ab1bb6493b15ec75e2e56cfd44bdda
Reviewed-on: https://chromium-review.googlesource.com/559029
Commit-Queue: Tsuyoshi Horo <horo@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#484241}
18 files changed