Disables show ntp at startup flag on Android

[SergeyZhukovsky]

Resolves brave/brave-browser#38635
Upstream enabled that flag by default on cr125 chromium/chromium@9e656e9

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:

I don't have exact steps, but usually it happens when you leave your browser for a long time(overnight)

[samartnik]

lgtm

[kjozwiak]

Verification PASSED on Pixel 6 Pro running Android 15 using the following build(s):

Brave | 1.69.91 Chromium: 127.0.6533.26 (Official Build) canary (64-bit)
--- | ---
Revision | c2e8b99455d26e792d29296a2f6dc7e1b80d913b
OS | Android 15; Build/AP31.240517.031; 35; REL

Prerequisites: For the following verification, I basically opened ~30 tabs (including several tab groups) and left Brave active on a random opened tab. After a certain amount of time, re-opened Brave and ensured that the correct tab is still active.

• re-opened after ~2hrs and ensured that the correct active tab is still active/selected when restoring
• re-opened after ~4hrs and ensured that the correct active tab is still active/selected when restoring
• re-opened after ~8hrs and ensured that the correct active tab is still active/selected when restoring
• re-opened after ~16hrs and ensured that the correct active tab is still active/selected when restoring