[iOS] Wrap HTTPS-by-default logic around feature flags

[kylehickinson]

Resolves brave/brave-browser#40634

Submitter Checklist:

• I confirm that no security/privacy review is needed and no other type of reviews are needed, or that I have requested them
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally:
  • npm run test -- brave_browser_tests, npm run test -- brave_unit_tests wiki
  • npm run presubmit wiki, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

[iefremov]

chromium_src ++

[ShivanKaul]

Just an update here that I'm chatting with @diracdeltas and @fmarier about whether we want this, let's not merge for now.
Update: fine to merge, brave/brave-browser#40634 captures the changes we need.

[kjozwiak]

Verification PASSED on iPhone 11 running iOS 17.5.1 via the following build(s):

Brave | 1.71.29 Chromium: 128.0.6613.85 (Official Build) nightly (64-bit) 
--- | ----
Revision | c532a6657223...
OS | iOS

Test Case #1 - brave://flags#https-only-mode enabled (default mode)

• ensured that brave://flags#https-only-mode is set as enabled by default on a clean/new install
• ensured Upgrade Connections to HTTPS is set as Standard as the default

Example	Example

While both brave://flags#https-by-default & brave://flags#https-only-mode are enabled, went through the STR/Cases outlined via brave/brave-browser#36408 (comment) as per the following:

Test interstitial

Example	Example	Example	Example	Example

Test upgrading

Example	Example	Example	Example	Example	Example

Test Case #2 - brave://flags#https-only-mode disabled

• disabled brave://flags#https-only-mode via brave://flags after installing 1.71.29 Chromium: 128.0.6613.85
• restart the browser once the brave://flag has been changed
• once disabled, ensured that Upgrade Connections to HTTPS is set as a boolean toggle (enabled/disabled)
• visited http://http.badssl.com and ensured that a interstitial page re: HTTP upgrade is NOT being displayed

Example	Example	Example

Test Case #3 - brave://flags#https-by-default disabled

• disabled brave://flags#https-by-default via brave://flags after installing 1.71.29 Chromium: 128.0.6613.85
• restart the browser once the brave://flag has been changed
• ensured that Upgrade Connections to HTTPS is set as a boolean toggle (enabled/disabled)
  • brave://flags#https-only-mode is also being disabled when brave://flags#https-by-default has been disabled
• visited http://http.badssl.com and ensured that a interstitial page re: HTTP upgrade is NOT being displayed
• ensured that http://brave.com --> https://brave.com
• ensured that http://google.com --> https://google.com
• ensured that http://facebook.com --> https://m.facebook.com
• ensured that http://reddit.com --> https://reddit.com

Example	Example	Example

Test Case #4 - brave://flags#https-only-mode being disabled but user has Strict selected

• installed 1.71.29 Chromium: 128.0.6613.85
• set Upgrade Connections to HTTPS as Strict via Settings
• disabled brave://flags#https-only-mode via brave://flags and restarted the browser
• ensured that the Upgrade Connections to HTTPS setting is now set as a boolean without Strict mode
• visited http://http.badssl.com and ensured that the interstitial page re: HTTP upgrade is NOT being displayed
• enabled brave://flags#https-only-mode via brave://flags and restarted the browser
• ensured that Upgrade Connections to HTTPS is now a drop down and Strict is being selected (users previous choice)
• visited http://http.badssl.com and ensured that the interstitial page is being used/displayed

RPReplay_Final1724640350.MP4