UserAgent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Firefox/52.0

Steps to reproduce the problem:
When deploying Linux distributions in networked environments with many clients, it's often advisable to use local package repository mirrors for installing software in order to save bandwidth and speed up downloading when running updates on several hundred clients simultaneously.

In order to achieve that, upstream repositories are mirrored using "debmirror" to make the repositories available locally. Then appropriate entries are added to the /etc/apt/sources.list.

Unfortunately, Google Chrome is one of the packages which forcefully installs its own google-chrome.list into /etc/apt/sources.list.d/ to add Google's own Debian package repositories.

The Debian package of the Opera webbrowser, on the other hand, provides such an option so that users with local mirrors can disable the automatic adding of Opera's official repositories:

root@zleih17:~> dpkg -l {google-chrome-stable,opera-stable}
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name                                  Version                 Architecture            Description
+++-=====================================-=======================-=======================-===============================================================================
ii  google-chrome-stable                  59.0.3071.115-1         amd64                   The web browser from Google
ii  opera-stable                          46.0.2597.26            amd64                   Fast and secure web browser
root@zleih17:~> debconf-get-selections |grep 'opera\|google-chrome'
opera-stable    opera-stable/add-deb-source     boolean false
opera   opera/add-deb-source    boolean false
root@zleih17:~>

What is the expected behavior?
Please add a debconf option for all Google Chrome Debian packages to disable the automatic adding of Google's Debian repositories.

What went wrong?
It's not possible to prevent the Debian package from adding Google's own repositories.

Did this work before? No 

Chrome version: 59.0.3071.115 (Official Build) (64-bit)  Channel: stable
OS Version: Debian Stretch 9.0
Flash Version: