Add worker related AppCache LayoutTests

Currently AppCache does work with dedicated workers and shared workers.
But according to the comment https://crbug.com/39368#c23, there are no LayoutTests.

To avoid introducing regressions on AppCache with workers by off-main-thread-fetch,
we need worker related AppCache LayoutTests.

Bug: 443374,39368
Change-Id: Ic1e3ecbb92e0fc51263dcb1f493a7778ba70e3ae
Reviewed-on: https://chromium-review.googlesource.com/558758
Commit-Queue: Tsuyoshi Horo <horo@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#484198}
7 files changed