Bypass http cache for concurrent range requests.

Take over of https://codereview.chromium.org/232003002/, which
instead utilizes the seemingly new cache timeout logic.

All partial requests which hit net::ERR_IO_PENDING will now be
immediately timed out.

BUG=31014
TEST=layout tests, net_unittests, new unittest, manual.

Review URL: https://codereview.chromium.org/478763004

Cr-Commit-Position: refs/heads/master@{#292031}
2 files changed