Enable an option to only use the secure Data Reduction Proxy when the secure proxy...

Enable an option to only use the secure Data Reduction Proxy when the secure proxy check succeeds.

Instead of being optimistic about using the secure proxy (i.e. use it unless
the check fails), flip the logic so that the secure proxy is not used unless
the check succeeds.

BUG=466753

Review URL: https://codereview.chromium.org/1132083004

Cr-Commit-Position: refs/heads/master@{#329961}