[OnionSoup] Move blink.mojom.FetchAPIResponse into blink/public/mojom/fetch/

This CL is the 2nd 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
- Remove the typemapping of blink.mojom.FetchAPIResponse.
  The mojom struct blink.mojom.FetchAPIResponse describes a Response in
  terms of the concept from the Fetch spec, currently it's defined under
  blink/public/platform/modules/fetch/ and is used only by Cache Storage
  API implementation (by both Browser and Renderer code), as this struct
  meets the 2 conditions below, it should be fine to go into
  blink/public/mojom/:
     - it is expected to be used by both Browser and Renderer code.
     - it is expected to be passed over Mojo between Browser and
       Renderer (Blink).
  But, currently for Chromium Mojo binding variant it is typemapped to
  content::ServiceWorkerResponse being used in
  content/browser/cache_storage/, this blocks it being moved to
  blink/public/mojom/. So we need to remove this typemapping first, this
  removal also helps reduce 1 user of content::ServiceWorkerResponse.

2nd step: (This CL)
  Now we can just move blink.mojom.FetchAPIResponse into
  blink/public/mojom/fetch/, which makes the next steps possible.

3rd step:
- Use blink.mojom.FetchAPIResponse to represent the response a service
  worker provides to FetchEvent#respondWith. Specifically, use this
  mojom struct to replace the existing [Native] mojom struct
  content.mojom.ServiceWorkerResponse in
  content/common/service_worker/service_worker_fetch_response_callback.mojom.
  Thus we can reduce another 1 user of content::ServiceWorkerResponse.
  More importantly, this makes it possible for us to move
  service_worker_fetch_response_callback.mojom into
  blink/public/mojom/service_worker/ in future.

4th step:
- 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: I9afad29a89887369c211cb46bce5bc98df16064f
Reviewed-on: https://chromium-review.googlesource.com/1149706
Commit-Queue: Han Leon <leon.han@intel.com>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579273}
10 files changed