Chrome Version       : 70.0.3528.4

Currently they're all mixed together, which makes for some mad dependency hell.

Context: https://chromium-review.googlesource.com/c/chromium/src/+/1186295/7/ui/file_manager/file_manager/background/js/test_util_base.js#546


https://chromium-review.googlesource.com/c/chromium/src/+/1188735 documents the current dependencies.

Plan to fix
 - create //ui/file_manager/toolkit
 - move things like //ui/file_manager/file_manager/background/js:background_base (and its dependencies) to this "toolkit"
  - also shared ui components, metadata, volume manager wrapper, etc.
 - eventually purge references to file_manager/file_manager from gallery, video_player, etc.
  - depend on the toolkit instead
   - file manager also depends on the toolkit