Later manipulation of Array.prototype.concat could lead to calling the Date constructor with empty arguments list. This let a non-mocked date slip in.

BUG=chromium:698097
NOTRY=true
TBR=yangguo@chromium.org,mstarzinger@chromium.org

Change-Id: Ib4bd97e06ea7be8c32d0057d42943f9f82ea6b5f
Reviewed-on: https://chromium-review.googlesource.com/449732Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43570}