Introduce To<FrameFetchContext>

Follow-up of https://chromium-review.googlesource.com/1352042

Bug: 880027
Change-Id: I1c289288239749bfd33e20bbdec948e6ab89512f
Reviewed-on: https://chromium-review.googlesource.com/c/1371045
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Hiroshige Hayashizaki <hiroshige@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615757}
3 files changed