The main timer functionality (get absolute time) is moved to common/ for
use in ANGLE itself (in upcoming overlay change).  util/Timer.h is no
longer an abstract class and uses this functionality to implement the
timer.

Bug: angleproject:3757
Change-Id: I3fe418778d80d1089c9bfe43a9e8098e43236f18
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1769061Reviewed-by: Cody Northrop <cnorthrop@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>