GitLab

We don't need it for keepalive requests any more, and
DetachableResourceHandler ignores cancel requests from renderer, which
is bad.

Change-Id: Iada35d44e2290760ed7b293cdd3dd7280e69edea
Bug: 836641
Reviewed-on: https://chromium-review.googlesource.com/1026333Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553480}