ozone/platform/wayland: Add WaylandTest base class to eliminate redundancy

Rather than have WaylandWindowTest, WaylandSurfaceFactoryTest, and soon
WaylandPointerTest all do the same setup, synchronization, and tear-down, just
use a common base class.

BUG=578890

Review URL: https://codereview.chromium.org/1740303002

Cr-Commit-Position: refs/heads/master@{#378724}
7 files changed