Intermittent crash if Confirmations library is called before being instantiated

[tmancey]

Fixes brave/brave-browser#7728

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Verified that these changes build without errors on
  • Android
  • iOS
  • Linux
  • macOS
  • Windows
• Verified that these changes pass automated tests (unit, browser, security tests) on
  • iOS
  • Linux
  • macOS
  • Windows
• Verified that all lint errors/warnings are resolved (npm run lint)
• Ran git rebase master (if needed).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Request a security/privacy review as needed.
• Add appropriate QA labels (QA/Yes or QA/No) to include the closed issue in milestone
• Public documentation has been updated as necessary. 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-Protection-Mode
  • 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-issues-with-tracking-protection
  • https://github.com/brave/brave-browser/wiki/QA-Guide

Test Plan:

• Confirm no crashes occur for Confirmations (see the console log)
• Confirm ads can be viewed and users are rewarded for a fresh install
• Confirm ads can be viewed and users are rewarded for an existing user profile
• Confirm ads can be viewed and users are rewarded for a recovered wallet
• Confirm ads can be viewed and users are rewarded after ads are switched off and then on

QA will also run through the following which also includes manual passes for ads:

• Manual test run on Android ARM for 1.7.0 Publisher data is now shown in panel after re-enabling Rewards from panel #2453 - https://github.com/brave/browser-android-tabs/issues/2453
• Manual test run on Android Tab for 1.7.0 (0.65.x) Upgrade from Chromium 74.0.3729.131 to Chromium 75.0.3770.38 #2455 - https://github.com/brave/browser-android-tabs/issues/2455

Reviewer Checklist:

• New files have MPL-2.0 license header.
• Request a security/privacy review as needed.
• Adequate test coverage exists to prevent regressions
• Verify test plan is specified in PR before merging to source

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.

[NejcZdovc]

rewards code looks good, didn't check other things

[tmancey]

Resolves Android crashes 1, 3, 5 and 6 for https://github.com/brave/browser-android-tabs/issues/2435 (which can also affecteds desktop users)

[LaurenWags]

Verified passed with macOS 10.14.6 x64 using

Brave	1.5.40 Chromium: 79.0.3945.117 (Official Build) nightly (64-bit)
Revision	04f0a055010adab4484f7497fbfdbf312c307f1d-refs/branch-heads/3945@{#1019}
OS	macOS Version 10.14.6 (Build 18G103)

• Verified test plan from Intermittent crash if Confirmations library is called before being instantiated #4370 (comment) (not including Android specific items)
• Confirmed no crashes observed for Confirmations in the terminal (staging and production)
• Confirmed no crashes observed for view, click, dismiss and landed (staging and production)
• Confirmed able to redeem tokens with the server without issue. (Staging)

Clean profile:

• Confirmed on the Ads panel on brave://rewards the Estimated pending rewards and Ad notifications received this month are incrementing as expected for a fresh profile. (Staging)
• Confirmed on the NTP widget that Estimated earnings so far this month is incrementing as expected for a fresh profile. (Staging)

Recovered wallet:

• Confirmed on the Ads panel on brave://rewards the Estimated pending rewards incremented as expected for a recovered wallet. (Staging)
• Confirmed on the NTP widget that Estimated earnings so far this month incremented as expected for a recovered wallet. (Staging)

Toggling Ads off/on:

• Confirmed able to view ads after Ads are switched off and then back on. (Staging and production)
• Confirmed on the Ads panel on brave://rewards the Estimated pending rewards and Ad notifications received this month are incrementing as expected after toggling Ads off and back on. (Staging and production)
• Confirmed on the NTP widget that Estimated earnings so far this month is incrementing as expected after toggling Ads off and back on. (Staging and production)

Existing/Upgraded profile:

• Confirmed on the Ads panel on brave://rewards the Estimated pending rewards and Ad notifications received this month are incrementing as expected for an upgraded/existing profile. (Production)
• Confirmed on the NTP widget that Estimated earnings so far this month is incrementing as expected for an upgraded/existing profile. (Production)