Don't report OnFirstSurfaceActivation for ui::Compositor

Bug: 893850
Change-Id: Iee754cefbd083d0a21a2b672fb8e837eaab81c43
Reviewed-on: https://chromium-review.googlesource.com/c/1293712
Reviewed-by: Antoine Labour <piman@chromium.org>
Commit-Queue: Saman Sami <samans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601629}