Have ResourceFetcher use a "detached" FetchContext when detached

Bug: 695939
Change-Id: I6afd1044629edb5771c28be162bd15bd63898863
Reviewed-on: https://chromium-review.googlesource.com/541117
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#481104}
5 files changed