GitLab

- move enums from ShelfLayoutManager to shelf_types.h
- remove redundant VisibilityState
- added SHELF_ prefix to these state.

BUG=151417
TEST=none

Review URL: https://chromiumcodereview.appspot.com/11316323

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@171024 0039d316-1c4b-4281-b951-d872f2087c98