GitLab

The function is no longer used since occlusion tracking is done
by aura::WindowOcclusionTracker.

Bug: 973682
Change-Id: I1bee51d47547f1e91f375c0f591dbd27664155de
Reviewed-on: https://chromium-review.googlesource.com/996299Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548400}