Add user visible flag for WebContentsOcclusion on Windows.

Bug: 813093
Change-Id: I8e4779551cb75d88f1f07c069cd7e5d7793da5b1
Reviewed-on: https://chromium-review.googlesource.com/c/1455094
Commit-Queue: David Bienvenu <davidbienvenu@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Fran├žois Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630102}
5 files changed