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This CL makes base::{Thread,Sequence}CheckerDoNothing noncopyable, so
that they are consistent to base::{Thread,Sequence}CheckerImpl, and an
accidental copy of SequenceChecker causes a compile error even on
DCHCEK-disabled build.

Change-Id: I3ac37d87302712ab3decf693d056376c0c2abb91
Reviewed-on: https://chromium-review.googlesource.com/578751
Commit-Queue: Taiju Tsuiki <tzik@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488614}