Fix units in comment in time_win.cc from milli to micro.
Fix units in comment in time_win.cc from milli to micro.

BUG=None

Review URL: https://codereview.chromium.org/1409863004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#354867}

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