Support upstream features override (in code) with ability to Griffin-override on top

The variations seed doesn’t support features state apply at the first start. We can implement some chromium_src-based change to alter the default state of Chromium features and still be able to control it via Griffin. Our current approach with appending --enable/disable-features doesn’t allow Griffin overrides.

Reasoning from @pes10k:

Could we change our deployment to make the features enabled by default in code, and then use griffin to disable only if needed? I know that for users it wont make a difference, but it’ll be increasingly important to make sure researchers / bloggers / measurers accurately understand and can replicate the privacy protections we’re providing.

Note: this does not replace master_preferences. The problem with master_preferences is that it’s not supported by selenium-webdriver for example. In reality, all experiments and research made with selenium-webdriver won’t get the actual features state we’re using in production.

[goodov]

Test cases

(1) Feature is enabled by default in Chromium, but disabled by default in Brave. Can be overridden via cmd line.

1. Ensure Brave doesn’t have Copy link to highlight context menu item when a text on a website is selected and a context menu is triggered (mouse right click).
2. Start Brave with --enable-features=CopyLinkToText
3. Expect the menu item is available.

(2) Feature is disabled by default in Chromium, but enabled by default in Brave. Can be overridden via cmd line.

1. Ensure there is Import passwords item on brave://settings/passwords in Saved Passwords section (click the three-dots button on the right).
2. Start Brave with --disable-features=PasswordImport.
3. Expect the item has disappeared.

(3) Control Brave-overridden feature using brave://flags.

1. Ensure there is Import passwords item on brave://settings/passwords in Saved Passwords section, make sure to cleanup command line after running test case #2.
2. Open brave://flags, change Password import flag state, relaunch browser.
3. Expect the item exists or doesn’t exist depending on the flag state.
4. Expect Default flag state shows the item.

[GeetaSarvadnya]

Verification PASSED on

Brave | 1.34.78 Chromium: 97.0.4692.71 (Official Build) (64-bit)
-- | --
Revision | adefa7837d02a07a604c1e6eff0b3a09422ab88d-refs/branch-heads/4692@{#1247}
OS | Windows 10 Version 21H2 (Build 19044.1415)

• Verified the test plan from https://github.com/brave/brave-browser/issues/18829#issuecomment-1004873247

Case 1: `Copy link to highlight` context menu

• Confirmed by default brave doesn’t have a Copy link to highlight context menu item when a text is selected on any website
• Confirmed Copy link to highlight context menu item is shown when a text is selected on any website when brave is launched using --enable-features=CopyLinkToText

brave default	brave with cmd line

Case 2: Import passwords

• Confirmed by default brave has Import option displayed in 3dot menu under Saved Passwords in brave://settings/passwords
• Confirmed 3dot menu with Import option is disappeared when brave is launched via cmd line --disable-features=PasswordImport

brave default	brave with cmd line

Case 3: Control `Import password` via brave://flags

• Confirmed enable/disable Import password option in brave://settings/passwords is controlled via brave://flags

Password import flag	Default or Enable	Disable

---

Verified using:

Brave | 1.34.78 Chromium: 97.0.4692.71 (Official Build) (x86_64)
-- | --
Revision | adefa7837d02a07a604c1e6eff0b3a09422ab88d-refs/branch-heads/4692@{#1247}
OS | macOS Version 11.6.1 (Build 20G224)

• Verified the test plan from https://github.com/brave/brave-browser/issues/18829#issuecomment-1004873247

Case 1: `Copy link to highlight` context menu - PASSED

• Confirmed by default Brave doesn’t have a Copy link to highlight context menu item when a text is selected on any website
• Confirmed Copy link to highlight context menu item is shown when a text is selected on any website when Brave is launched using --enable-features=CopyLinkToText

brave default	brave with cmd line

Case 2: Import passwords - PASSED

• Confirmed by default Brave has Import option displayed in 3dot menu under Saved Passwords in brave://settings/passwords
• Confirmed 3dot menu with Import option is disappeared when Brave is launched via cmd line --disable-features=PasswordImport

brave default	brave with cmd line

Case 3: Control `Import password` via brave://flags - PASSED

• Confirmed enable/disable Import password option in brave://settings/passwords is controlled via brave://flags

Password import flag - Default	Password import flag - Enable	Password import flag - Disable