GitLab

Modifier flags needs same treatment as pressed keys. Move modifier flag
tracking to Seat class.

Bug: 788731
Tbr: yoshiki@chromium.org
Test: exo_unittests --gtest_filter=KeyboardTest.OnKeyboardEnter
Change-Id: Ife2fae2d622dfff3617830ba232d0267fdbc9b35
Reviewed-on: https://chromium-review.googlesource.com/805359Reviewed-by: David Reveman <reveman@chromium.org>
Commit-Queue: David Reveman <reveman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521257}