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There was a fear that the value iterator was flaky on Win 7. If that's
true, a little test coverage should expose it.

BUG=1066801
R=robliao@chromium.org

Change-Id: I984044243886510c9c540bc471b6a62a26212e3e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2540447
Commit-Queue: Greg Thompson <grt@chromium.org>
Auto-Submit: Greg Thompson <grt@chromium.org>
Reviewed-by: Robert Liao <robliao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828395}