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This CL replaces CHECK with DCHECK to prevent fatal failures in the wild.

TBR=asvitkine@chromium.org

Bug: 910833
Change-Id: I070339cb47506b2b6823b9d3f8e4a7b06fc310ff
Reviewed-on: https://chromium-review.googlesource.com/c/1357919Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Commit-Queue: Alexander Alekseev <alemate@chromium.org>
Cr-Commit-Position: refs/heads/master@{#613314}