[Background Fetch] Move non-forwarding logic out of delegate proxy

The delegate proxy should just communicate with the delegate.
RequestInfos are moved to the job controllers.

Bug: 850512
Change-Id: I1002db53225d2b7ade3b6a40549946de120cae79
Reviewed-on: https://chromium-review.googlesource.com/c/1422158
Commit-Queue: Rayan Kanso <rayankans@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Reviewed-by: Mugdha Lakhani <nator@google.com>
Cr-Commit-Position: refs/heads/master@{#629167}
6 files changed