Don't show default browser prompt if other brave channel is already set as a default

[simonhong]

If brave's any channel is already set as a default browser, the other installs should not show default browser prompt.

[kjozwiak]

@simonhong does this include Win? Or is this specifically for macOS & Linux? If it's for all platforms, we can remove the OS/Linux & OS/macOS labels and just keep OS/Desktop so it gets checked on all three.

Assuming this includes Win x64 as per

windows checks:
https://source.chromium.org/chromium/chromium/src/+/master:chrome/installer/util/shell_util.cc;l=1246

[simonhong]

@kjozwiak This issue is only for mac/linux because we already have cross channel checking logic for Windows.

[btlechowski]

QA/Blocked as we also need release channel build

[btlechowski]

No longer QA/Blocked as we have a 1.21.x release build.

[stephendonner]

Verified FIXED using

Brave	1.21.68 Chromium: 89.0.4389.58 (Official Build) (x86_64)
Revision	1a139f28ecc27719439e37c6b1533cee999cb802-refs/branch-heads/4389@{#1134}
OS	macOS Version 11.2.2 (Build 20D80)

Verified the testplan from brave/brave-core#7841.

Verified default-browser prompt is not shown when:

• Brave release is the default browser, launching beta, dev, nightly
• Brave nightly, dev, or beta is the default browser, launching release

Verified default-browser prompt is shown when:

• Firefox is the default browser
• Chrome is the default browser
• Safari is the default browser

I also verified that when other Brave channels are set as default, the Make default button shows up in release, brave://settings/ as it should.

---

Verification passed on

Brave	1.21.70 Chromium: 89.0.4389.69 (Official Build) (64-bit)
Revision	6df9174a477a0bea2118cb4669954d517be16104-refs/branch-heads/4389@{#1332}
OS	Ubuntu 18.04 LTS

Verified test plan from brave/brave-core#7841

Brave release default
beta - verified no prompt, verified Make default button shows up in brave://settings/
dev - verified no prompt, verified Make default button shows up in brave://settings/
nightly - verified no prompt, verified Make default button shows up in brave://settings/

Brave beta default
release - verified no prompt, verified Make default button shows up in brave://settings/
dev - verified no prompt, verified Make default button shows up in brave://settings/
nightly - verified no prompt, verified Make default button shows up in brave://settings/

Brave dev default
release - verified no prompt, verified Make default button shows up in brave://settings/
dev - verified no prompt, verified Make default button shows up in brave://settings/
nightly - verified no prompt, verified Make default button shows up in brave://settings/

Brave nightly default
release - verified no prompt, verified Make default button shows up in brave://settings/
dev - verified no prompt, verified Make default button shows up in brave://settings/
nightly - verified no prompt, verified Make default button shows up in brave://settings/

Verified default-browser prompt is shown for release, beta, dev, nightly when:
Firefox is the default browser
Chrome is the default browser