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After all surfaces are detached, the model is eventually unloaded.
The timeout used is configurable via finch parameter.

Bug: 1044139
Change-Id: I015945215c1a0cc25fff92ccf20a5d72f52c7309
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2216037
Commit-Queue: Dan H <harringtond@chromium.org>
Reviewed-by: Carlos Knippschild <carlosk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#772956}