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With this change, the paint preview base service now can (optionally)
be passed a policy object which can disallow paint previews for which
it is not well suited.

Bug: 1026349
Change-Id: I2dc9707fe17ca076c95f7ebdf0d064a710bb3b9b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1986615
Commit-Queue: Ian Vollick <vollick@chromium.org>
Reviewed-by: Calder Kitagawa <ckitagawa@chromium.org>
Cr-Commit-Position: refs/heads/master@{#728304}