[files-cleanup] Rename file providers for consistency.

The four file providers are to be named:
- zero state file
- zero state drive
- file search
- drive search

This should have no user visible effect.

Bug: 1188495
Change-Id: I3d5fdac845a5cf2e0dabc6f4b4907ff8a746fc2d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2771524


Reviewed-by: Tony Yeoman <tby@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Rachel Wong <wrong@chromium.org>
Cr-Commit-Position: refs/heads/master@{#864950}