[PWA] Fix GetOriginsWithInstalledWebApps, add tests

Fixed: b:348445406
Change-Id: I5346f7e6a89d54403ca8a80c6b967238b9a0f04b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5735615


Auto-Submit: Daniel Murphy <dmurph@chromium.org>
Commit-Queue: Daniel Murphy <dmurph@chromium.org>
Reviewed-by: Ayu Ishii <ayui@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1331905}