DLP: Reenable test to check caller

Starting SelectFileDialogExtension is more complicated than expected
because there's no way to check if the files app is open unless we
redo the same work in SelectFileDialogExtensionBrowsertest which I
think is useless to repeat, so I only kept the test to check for the
caller that it's passed as expected.

Bug: b/260314212
Change-Id: I5a8a981e05ccf96ed48597006904fa99c633aeee
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4061620


Reviewed-by: Aida Zolic <aidazolic@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Auto-Submit: Aya Elsayed <ayaelattar@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1077095}