Re-enable ReportingObserver and make noop

[ShivanKaul]

Resolves brave/brave-browser#39759

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:

See brave/brave-browser#39759

[emerick]

chromium_src++

[kjozwiak]

Verification PASSED on Win 11 x64 using the following build(s):

Brave | 1.70.12 Chromium: 127.0.6533.57 (Official Build) nightly (64-bit)
-- | --
Revision | 5755980f479ca93ac5b74023fad08fb5556a5503
OS | Windows 11 Version 23H2 (Build 22631.3880)

Using the STR/Cases outlined via brave/brave-browser#39759 (comment), ensured that LastPass was working correctly as per the following:

• ensured that LastPass can be installed/launched via https://chromewebstore.google.com/detail/lastpass-free-password-ma/hdokiejnpimakedhajhdlcegeplioahd without any issues
• ensured that tapping on the LastPass icon opened the panel without any issues
• ensured that LastPass is autofilling saved passwords without any issues
  • used https://leagueofcomicgeeks.com/login as a quick check in this instance
• ensured that selecting the Username or Password field for a website with a saved password correctly loads LastPass
  • ensured that you can fill in the credentials via selecting either the Username or Password from a field

Example	Example	Example	Example