Temporary fix to prevent the DRP from being activated improperly.

Temporary fix to prevent the DRP from being activated improperly.

This change prevents any *.googlezip.net Data Reduction Proxy from being
configured as part of the ProxyService's ProxyConfig via the
proxy pref.

Specifying a DRP in the proxy rules is not a supported means of
activating the DRP, and could cause requests to be sent to the DRP
without the appropriate authentication headers and without using any of
the DRP bypass logic.

This is a fix for http://crbug.com/476610, to be merged into M43.

BUG=476610

Review URL: https://codereview.chromium.org/1126413006

Cr-Commit-Position: refs/heads/master@{#329349}