Fix all failed and canceled URLRequestStatuses without errors.

As a step towards removing URLRequestStatus::Status, stop creating FAILED
and CANCELED URLRequestStatuses without supplying an error.

IO_PENDING is left for later as that'll want a bit more careful auditing of
error() callers.

BUG=490311

Review URL: https://codereview.chromium.org/1239993004

Cr-Commit-Position: refs/heads/master@{#341913}
23 files changed