Initial hookup of CSS prefers-reduced-motion for Mac/Win

For now, the hookup is static; changing the OS level settings will not
cause the settings to be recalculated.

Test: Manually verified functional on Mac and Windows.
Bug: 722548
Change-Id: Iccb601a28d26a7ac659677041ce637bdd19e7db3
Reviewed-on: https://chromium-review.googlesource.com/c/1417754
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Ian Vollick <vollick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625249}
12 files changed