The timezone part of the Date string representation might contain
non-ASCII characters depending on the exact platform configuration,
so we cannot safely assume that the whole date string is ASCII
encoded.

CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_chromium_rel_ng;tryserver.blink:linux_blink_rel
R=yangguo@chromium.org
BUG=chromium:581925
LOG=n

Review URL: https://codereview.chromium.org/1838063002

Cr-Commit-Position: refs/heads/master@{#35089}