Mark three new dialog tests as slow tests
These all seems to flaky-fail with a timeout on some Mac platforms.
Mark them slow tests to give them more time.
Fixed: 377943753,379418916
Change-Id: Idfe412cfacd521894dde745cd788d803ac27c719
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6033672
Commit-Queue: Di Zhang dizhangg@chromium.org
Auto-Submit: Mason Freed masonf@chromium.org
Reviewed-by: Di Zhang dizhangg@chromium.org
Cr-Commit-Position: refs/heads/main@{#1384687}