Fixes ad conversion detection fails if the target URL of the last shown ad matches the conversion URL pattern

[tmancey]

Resolves brave/brave-browser#8362

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
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  • 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:

• See Ad conversion detection fails if the target URL of the last shown ad matches the conversion URL pattern brave-browser#8362

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.

[tmancey]

CheckAdConversion should be called for every call to OnPageLoaded otherwise ad conversion detection failed if the target URL of the last shown ad matches the conversion URL pattern

[emerick]

LGTM

[btlechowski]

LGTM

brave/brave-browser#8362 (comment)

Logged brave/brave-browser#8648 for a special case