Only hide sidebar when tab-initiated fullscreen mode

[simonhong]

Resolves brave/brave-browser#16160

Submitter Checklist:

• I confirm that no security/privacy review is needed, or that I have requested one
• 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, npm run lint, 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/Custom-Headers
  • 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:

1. Launch browser and check sidebar is visible
2. Load youtube.com and play anything.
3. Change to youtube fullscreen mode by pressing f key
4. Check sidebar is not visible
5. Pressing esc to exit fullscreen mode check sidebar is visible again
6. Make browser maximized windows by using window button
7. Check sidebar is still visible

[sangwoo108]

LGTM 👍

[kjozwiak]

Reproduced the original issue on macOS 12.5.1 x64 Monterey using the following build(s):

Brave | 1.45.5 Chromium: 105.0.5195.52 (Official Build) nightly (x86_64)
--- | ---
Revision | 412c95e518836d8a7d97250d62b29c2ae6a26a85-refs/branch-heads/5195@{#853}
OS | macOS Version 12.5.1 (Build 21G83)

Ran through the STR/Cases via #14790 (comment) and reproduced the issue re: the sidebar not being visible once you maximize the browser to full screen as per the following:

Verification PASSED on macOS 12.5.1 x64 Monterey using the following build(s):

Brave | 1.45.8 Chromium: 105.0.5195.58 (Official Build) nightly (x86_64)
--- | ---
Revision | 1907e1693887af4463221a10247360b7a056db49-refs/branch-heads/5195_47@{#3}
OS | macOS Version 12.5.1 (Build 21G83)

As per the above, originally reproduced the issue and using the STR/Cases outlined via #14790 (comment) and ensured it wasn't occurring with 1.45.8 Chromium: 105.0.5195.58 which has the fix as per the following:

• ensured that the sidebar was being displayed on first launch via brave://welcome
• ensured that the sidebar was being displayed when visiting YT
• ensured that the sidebar wasn't being displayed viewing media/YT video via fullscreen
• ensured that the sidebar was being displayed once you exit fullscreen (watching a video)
• ensured that the sidebar is visible when going into fullscreen (maximize browser window)
• ensured that the sidebar is visible when exiting fullscreen (maximize browser window)

Example	Example	Example	Example	Example