Introduce FetchContext::Bind

As a preparation to split FetchContext, this CL adds Bind/Unbind
functions to bind FetchContext with ResourceFetcher.

Bug: 914739
Change-Id: Id1bc8c86117d4ac306563c9ab197c9c12440ce71
Reviewed-on: https://chromium-review.googlesource.com/c/1388055
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@{#621463}
5 files changed