EXO: Refactor input timestamps manager interface

Move input timestamps manager out of server.cc
This CL only moves code around.

Bug: 896710
Test: Built on ChromeOS
Change-Id: I65e8baba6d20b726cf69fed3b90286d6ea7cd756
Reviewed-on: https://chromium-review.googlesource.com/c/1318789
Commit-Queue: Shawn Gallea <sagallea@google.com>
Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608228}
4 files changed