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This is useful to be able to call non-const methods on an object owned
by a SequenceBound, while disallowing the SequenceBound owner itself
from being mutated via Reset() and the like.

Bug: 1140588
Change-Id: I32924106c061b4b7916885fc6fe14462b43484e5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2487822
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819473}