Chrome Cleanup UI: Extract GetLastUsedProfile call from scanner results

Chrome runs into a fatal error when the cleaner detects unwanted
software. This is because ChromeCleanerScannerResults is created in the
IO thread, and ProfileManager::GetLastUsedProfile requires the UI
thread. The tests passed because they run a test browser process.

- Extract extension name fetching to a separate function.
- Call this function in tests so they're not affected.
- Follow-up CL: Call this function once the scanner results are on the
UI thread, before they're sent to the web UI.

Bug: 853339
Change-Id: I9cc2425f7b196e923a22b2afd1e8eee7fca61f5b
Reviewed-on: https://chromium-review.googlesource.com/1135194
Commit-Queue: Nick Burris <nburris@google.com>
Reviewed-by: proberge <proberge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574695}
4 files changed