Launch first run dialog on macOS and linux

[simonhong]

Resolves brave/brave-browser#12679

Development build doesn't launch this dialog.(https://github.com/brave/brave-core/pull/7700/files#diff-edfdf2e925a57fc30614d6d3ee529e49a5d9d29afe5eef326f1a83f09b456818R32)

On macOS:

On linux:

Submitter Checklist:

• There is a ticket for my issue.
• Used Github auto-closing keywords in the commit message.
• Wrote a good PR/commit description
• 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).
• Requested a security/privacy review as needed.

Reviewer Checklist:

• 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. Start Browser with clean profile and check first run dialog is launched.
2. If default is checked, macOS asks about replacing default browser (linux doesn't ask more for replacing default browser)
3. If reporting check box is set, p3a and crash report option are turned on
4. If reporting check box is unset, p3a and crash report option are turned off.

[iefremov]

Implementation looks good, just want to double-check presence of P3A in this dialog, see Slack https://bravesoftware.slack.com/archives/CDNJ9SVUL/p1611956161037900

[karenkliu]

Looks good! 👍

[simonhong]

Kindly ping to @brave/patch-reviewers :)

[mkarolin]

++ on chromium_src

[simonhong]

AdBlockServiceTest.CosmeticFilteringProtect1p was failed only on Windows CI but it's unrelated with this PR.