[Desktop] Installing Brave on a Debian system with Chrome doesn't automatically set Brave as the default

[fmarier]

When a user installs Chrome on Debian, it automatically becomes the default given that Chrome has chosen an alternative priority above all other browsers. On the other hand, when a user installs Brave, it doesn't automatically become the default.

Given we expect more users to install Chrome first and then later switch to Brave, I think it makes sense to follow Chrome's lead and bump the alternative priority.

This is what the x-www-browser alternative looks like on my machine:

$ sudo update-alternatives --config x-www-browser
There are 7 choices for the alternative x-www-browser (providing /usr/bin/x-www-browser).

  Selection    Path                              Priority   Status
------------------------------------------------------------
  0            /usr/bin/brave-browser-stable      200       auto mode
* 1            /usr/bin/brave-browser-beta        150       manual mode
  2            /usr/bin/brave-browser-dev         0         manual mode
  3            /usr/bin/brave-browser-nightly     0         manual mode
  4            /usr/bin/brave-browser-stable      200       manual mode
  5            /usr/bin/chromium-browser-stable   200       manual mode
  6            /usr/bin/firefox                   40        manual mode
  7            /usr/bin/google-chrome-stable      200       manual mode

Note: the priority is only taken into account when the user hasn't made a selection. A user's choice is never overridden.

[btlechowski]

Verification passed on

Brave	1.14.68 Chromium: 85.0.4183.83 (Official Build) dev (64-bit)
Revision	94abc2237ae0c9a4cb5f035431c8adfb94324633-refs/branch-heads/4183@{#1658}
OS	Ubuntu 18.04 LTS

Verified test plan from brave/brave-core#6253