Fixed crash when fetching Rewards Widget estimated earnings

[tmancey]

Resolves brave/brave-browser#14447

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
• 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:

• Confirm Rewards Widget estimated earnings are updated after a fresh install
• Confirm Rewards Widget estimated earnings are updated after viewing at least 1 ad
• Confirm Rewards Widget estimated earnings are updated after refreshing a new tab page
• Confirm "Restarting ads service" does not appear in the console logs

[emerick]

LGTM

[moritzhaller]

LGTM

[tmancey]

CI failed for known audit dep issue

[kjozwiak]

Verification PASSED on Win 10 x64 using the following build:

Brave | 1.23.24 Chromium: 89.0.4389.82 (Official Build) nightly (64-bit)
-- | --
Revision | 8d785cc4e2b89bff35f6a21710215271fb8fd782-refs/branch-heads/4389@{#1433}
OS | Windows 10 OS Version 2009 (Build 19042.844)

• ensured that clicking on Startg using Rewards via brave://newtab works as expected
• ensured that estiamted earnings is being updated in a previously opened brave://newtab after viewing an ad
• ensured that the correct estimated earnings is being displayed when opening a new brave://newtab after viewing an ad
• ensured that refreshing brave://newtab right after viewing an ad doesn't crash Brave and updates estiamted earnings correctly
• ensured that that estimated earnings under brave://rewards match the value that's being displayed under brave://newtab
• ensured that Restarting ads service isn't appearing in the CLI/terminal logs

However, ran into brave/brave-browser#14143 while running through the above which appears to be a known issue and not a new regression due to the above PR.

[tmancey]

@kjozwiak I did not see the above ticket as it was assigned to the rewards project, however I have closed brave/brave-browser#14143 as it is a duplicate of brave/brave-browser#13267