Restore the 'BlockCredentialedSubresources' runtime flag.

There's some negative feedback flowing in as the change hits stable, so.
Let's put the flag back for the time being.

Bug: 731618
Change-Id: If37bd732e9e2b364cd1eedeedbb85838602453d3
Reviewed-on: https://chromium-review.googlesource.com/535521
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Commit-Queue: Mike West <mkwst@chromium.org>
Cr-Commit-Position: refs/heads/master@{#479478}
3 files changed