[OnionSoup] Remove [Native] content.mojom.ServiceWorkerResponse

This CL is the 4th step of the plan below aiming to eliminate the native
struct content::ServiceWorkerResponse defined in
content/common/service_worker/service_worker_types.h.

1st step:
https://chromium-review.googlesource.com/c/chromium/src/+/1134731

2nd step:
https://chromium-review.googlesource.com/c/chromium/src/+/1149706

3rd step:
https://chromium-review.googlesource.com/c/chromium/src/+/1155999

4th step: (this CL)
- Use blink.mojom.FetchAPIResponse to represent responses to background
  fetches. Specifically, use this mojom struct to replace the existing
  [Native] mojom struct content.mojom.ServiceWorkerResponse defined in
  content/common/service_worker/service_worker.mojom.
  Thus we can reduce the last 1 user of content::ServiceWorkerResponse.

5th step:
- Remove content::ServiceWorkerResponse and do any left cleanup.

BUG=789854

Change-Id: I85e6e9489dac50e1cc6905bd28a2d47b7a90fde7
Reviewed-on: https://chromium-review.googlesource.com/1164848
Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582489}
11 files changed