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Those files are said to be ChromeOS only, putting all of them
into _chromeos.cc files and removing others. _ozone, _win, and
_x11 are actually referring to _mus, but they won't be used since
the feature isn't enabled on those platforms.

Bug: 867078
Test: build passes
Change-Id: I76e7285fce7aac7c229a7cbe8668c5f654276178
Reviewed-on: https://chromium-review.googlesource.com/1149186
Commit-Queue: Jun Mukai <mukai@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577980}