Enable multiple WorkerFetchContext per one global scope

Currently WorkerFetchContext has the ownership of
some objects originated from WebWorkerFetchContext.
To create multiple WorkerFetchContexts
for one WorkerOrWorkletGlobalScope/WebWorkerFetchContext,
this CL moves these ownership outside WorkerFetchContext.
- url_loader_factory_ and script_loader_factory_
  from WorkerFetchContext to WebWorketFetchContext subclasses, and
- subresource_filter_ from WorkerFetchContext to
  Still |WorkerFetchContext::subresource_filter_| is kept, but
  it is created in WorkerOrWorkletGlobalScope and passed to

This CL doesn't change the observable behavior.
This CL creates WebURLLoaderFactory a little more eagerly, i.e.
when WorkerFetchContext is created,
while previously it was created when
WorkerFetchContext::CreateURLLoader() is called for the first time.

Bug: 880027, 903579
Change-Id: I84a8bafee25b7f293201a271d198260e2dfb8e68
Reviewed-on: https://chromium-review.googlesource.com/c/1193385
Commit-Queue: Hiroshige Hayashizaki <hiroshige@chromium.org>
Reviewed-by: Tsuyoshi Horo <horo@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606835}
9 files changed