Add CHECKs to debug crbug.com/916098

This adds CHECKs to all loaders that are not null checked before calling
ResumeReadingBodyFromNet, which will hopefully give a better stack so we
can find the real culprit.

Bug: 916098
Change-Id: I11f01f6bffe44dd17efb16f9c89ee5d6bd078d5c
Reviewed-on: https://chromium-review.googlesource.com/c/1471210
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Clark DuVall <cduvall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632011}
7 files changed