stats: Add dtoi param to usage ping

[kkuehlz]

Resolves brave/brave-browser#10061

Resolves

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-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-issues-with-tracking-protection
  • https://github.com/brave/brave-browser/wiki/QA-Guide

Test Plan:

1. Open network sniffing tool (Charles, Wireshark)
2. Ensure that the browser sends a request to https://laptop-updates.brave.com/1/usage/brave_core with query parameter set to the current date
3. Move system clock forward 14 days and see that this parameter is sent up as null.

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.

[kkuehlz]

Spec is here https://docs.google.com/document/d/1iSYi_i52dP6YGdrUhP7J7DMBzxyPf9x6nFpg422LfLo/edit

[kkuehlz]

cc @emerick I went ahead and refactored the referral code to be part of the shared stats utils. Reading the sentinel actually won't block (left comment), so it ends up working out nicely without callbacks. I'm thinking we get this merged first, and I'll rebase #5721 on master and have the referral factory use this method and pass the result to the ctor (as @simonhong has suggested for other shared code).

[emerick]

LGTM, just one minor comment.

[bbondy]

Just a reminder to please set the milestone on PRs for the milestone they are landing in.
I updated this time.

[kjozwiak]

Verification PASSED on macOS 10.15.5 x64 Catalina using the following build:

Brave | 1.12.77 Chromium: 84.0.4147.68 (Official Build) nightly (64-bit)
-- | --
Revision | e7b7234037639b407e69c5428c891ce018cd6c0d-refs/branch-heads/4147@{#772}
OS | macOS Version 10.15.5 (Build 19F101)

Ensured that dtoi=2020-07-07 on initial install as per the following:

https://laptop-updates.brave.com/1/usage/brave-core?platform=osx-bc&channel=nightly&version=1.12.72&daily=true&weekly=true&monthly=true&first=true&woi=2020-07-06&dtoi=2020-07-07&ref=BRV001

Moved the MBP time ~14 days ahead and ensured that dtoi=null as per the following:

https://laptop-updates.brave.com/1/usage/brave-core?platform=osx-bc&channel=nightly&version=1.12.72&daily=true&weekly=true&monthly=false&first=false&woi=2020-07-06&dtoi=null&ref=BRV001