Introduce ResourceFetcherInit

... to get more flexibility on ResourceFetcher construction. Also remove
Archive() and InitialThrottlingPolicy() from FetchContext because they
are used only in ResourceFetcher construction.

Bug: 914739
Change-Id: I14e822632c0ceab32c6e0c161f63f32a44e9d517
Reviewed-on: https://chromium-review.googlesource.com/c/1391036
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Hiroshige Hayashizaki <hiroshige@chromium.org>
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621880}
12 files changed