Enable strict site isolation by default

[jumde]

brave/browser-laptop#14766

[bbondy]

We have this enabled by default now with C68

[diracdeltas]

@bbondy it shows up still as disabled in chrome://flags/#enable-site-per-process

tested on MacOS Version 0.53.0 Chromium: 68.0.3440.68 (Official Build) dev (64-bit)

[bbondy]

Per the steps here:
https://www.chromium.org/Home/chromium-security/site-isolation#TOC-Verifying

I believe it's enabled. I think the chrome://flags setting is no longer used.
You can also see a quick recap on chrome://process-internals which shows it working.
I verified with Chrome's task manager with the test case they describe above though and it seems to be working correctly.

Let me know if I'm missing something or not though, it wouldn't be hard to also enable that flag. But I think the UI for the flag will be removed in an upcoming Chromium version. Unless I'm not understanding that the flag does something extra. Please lmk @diracdeltas. Thanks for checking!

[diracdeltas]

if the listed test plan works, closing this sgtm.

if there is a more general issue that chrome://flags in brave doesn't reflect reality, we should either fix that or at least put a disclaimer on chrome://flags.

[btlechowski]

Verification passes on

Brave	0.55.6 Chromium: 70.0.3538.16 (Official Build) dev (64-bit)
Revision	16ed95b41bb05e565b11fb66ac33c660b721f778-refs/branch-heads/3538@{#306}
OS	Windows 7

Checked chrome://process-internals and test case from https://www.chromium.org/Home/chromium-security/site-isolation#TOC-Verifying

Verification passes on

Brave	0.55.6 Chromium: 70.0.3538.16 (Official Build) dev (64-bit)
Revision	16ed95b41bb05e565b11fb66ac33c660b721f778-refs/branch-heads/3538@{#306}
OS	Linux

• Verified steps from https://www.chromium.org/Home/chromium-security/site-isolation#TOC-Verifying

Verified passed with

Brave	0.55.10 Chromium: 70.0.3538.22 (Official Build) beta(64-bit)
Revision	ac9418ba9c3bd7f6baaffa0b055dfe147e0f8364-refs/branch-heads/3538@{#468}
OS	Mac OS X

• Verified steps from https://www.chromium.org/Home/chromium-security/site-isolation#TOC-Verifying