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This is part of a series moving IO on evdev devices to a fast thread,
since UI thread is too slow for the cursor.

EventModifiersEvdev is a UI thread object, so move all remaining
ui::Event construction outside of the device-specific objects. Devices
no longer get a EventModifiersEvdev* since they will execute on a
different thread.

This completes the series moving ui::Event construction out of device
objects and into EventFactoryEvdev.

BUG=449710
TEST=boot link_freon & click mouse

Review URL: https://codereview.chromium.org/867803004

Cr-Commit-Position: refs/heads/master@{#313464}