Add support for specifying custom enable/disable feature switches

[mrzealot]

I've found a diff between how Chromium and Brave handle console messages over the devtools protocol where console events from a non-top-level frame are not transmitted to the remote debugging entity in Brave. This leads back to how strict site-per-process isolation is handled; at least, specifying --site-per-process on Chromium makes it behave like Brave in that they are both "wrong" from the console messages' POV. Making them both "right" would probably require setting --disable-features=IsolateOrigins,site-per-process as per these docs, but Brave overrides this flag here.

I think this could be solved by being able to set custom disable switches, but there could be other interactions in the background I'm not aware of yet. Can share a MWE to test console event on the remote side if needed.

[iefremov]

It seems that base::CommandLine can't merge two --disable-features switches

[mkarolin]

@iefremov, exactly: https://cs.chromium.org/chromium/src/base/command_line.cc?q=CommandLine::AppendSwitchNative&sq=package:chromium&g=0&l=344 - if the switch already exists the value is just overwritten with the new one.

[btlechowski]

Verification passed on

Brave	0.61.38 Chromium: 73.0.3683.39 (Official Build) beta (64-bit)
Revision	cc53b0e12fcaf42e4bab8d6c23bd4fb7aae99f6c-refs/branch-heads/3683@{#413}
OS	Windows 7 Service Pack 1 Build 7601.24312

Default:

With --disable-features=IsolateOrigins,site-per-process flag

Verification passed on

Brave	0.61.41 Chromium: 73.0.3683.39 (Official Build) beta (64-bit)
Revision	cc53b0e12fcaf42e4bab8d6c23bd4fb7aae99f6c-refs/branch-heads/3683@{#413}
OS	Linux Mint

• Verified description mentioned in the issue.
• Navigation to chrome://process-internals/#general causing webview crash. Logged Folllow up of #3209 - Navigation to chrome://process-internals/#general is causing webview crash #3579

Default:

With --disable-features=IsolateOrigins,site-per-process flag

Verifications PASSED on macOS 10.14.3 x64 using the following build:

Brave	0.61.45 Chromium: 73.0.3683.39 (Official Build) beta(64-bit)
Revision	cc53b0e12fcaf42e4bab8d6c23bd4fb7aae99f6c-refs/branch-heads/3683@{#413}
OS	Mac OS X

Default:

Using the --disable-features=IsolateOrigins,site-per-process flag

[kjozwiak]

Navigation to chrome://process-internals/#general causing webview crash

@GeetaSarvadnya did you create an issue for the above? Looks like it's only happening when you launch Brave using --disable-features=IsolateOrigins,site-per-process and visit chrome://process-internals/#general instead of brave://process-internals/#general. If you haven't, please create a new issue and CC @mkarolin. Reproduced on macOS 10.14.3 x64 as well.