GitLab

Using Mojo for blob handles has recently been enabled, but the
Background Fetch code hadn't been updated yet. In effect, responses
originating from Background Fetches started hitting a DCHECK.

BUG=

Change-Id: I0e4d765eb8ae42f02144261ba517b134be432ece
Reviewed-on: https://chromium-review.googlesource.com/746921
Commit-Queue: Peter Beverloo <peter@chromium.org>
Reviewed-by: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#513113}