Pickers: Convert enums to IntDefs.

Bug: None
Change-Id: Ib0b805cd28e7e45f533d93f22d893e4298407b8a
Reviewed-on: https://chromium-review.googlesource.com/c/1273526
Commit-Queue: Finnur Thorarinsson <finnur@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#598752}