Treat '...' as a non-parent path component outside of Windows.

https://codereview.chromium.org/12771015 made FilePath::ReferencesParent treat
'...' as an illegal path component due to bizarre Windows behaviors, but '...'
is a reasonable path component on UNIX. Condition that logic on OS_WIN.

BUG=464760

Review URL: https://codereview.chromium.org/1469153006

Cr-Commit-Position: refs/heads/master@{#361764}
3 files changed