Fix DCHECK in CrashDirectoryWatcher

We use base::FileEnumerator to watch for changes in our crash
directory using a combination of FILES | NAME_ONLY. For whatever
reason, base::FileEnumerator doesn't allow NAME_ONLY to be
combined with FILES and DCHECKs. I was running an official, release
build for testing since that is where breakpad is enabled so I
missed this DCHECK during development.

Change-Id: I2c5033eb995bca6eb26572f7bc60c7fef36c555e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4550040


Auto-Submit: Joe Downing <joedow@chromium.org>
Reviewed-by: Lambros Lambrou <lambroslambrou@chromium.org>
Commit-Queue: Joe Downing <joedow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1146751}