VC++ 2017's STL doesn't suppress warnings as aggressively as prior
versions did. This causes warnings on code which mixes signed and
unsigned types. In this case a deque of unsigned integers was being
queried to see how many signed integers it contains. This could be
fixed by passing in unsigned 0, 1, and 2 to std::count but changing
the deque from unsigned to int is simpler.

R=adamk@chromium.org
BUG=chromium:683729

Review-Url: https://codereview.chromium.org/2834293002
Cr-Commit-Position: refs/heads/master@{#44814}