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Similar to Oilpan, only return a struct of callbacks and don't actually
call further into visitors.

Bug: chromium:802273
Change-Id: Idd8cae4492876ddfda2bc6b438e4939825f32cdf
Reviewed-on: https://chromium-review.googlesource.com/945788
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#540846}