Track occluded region in WindowOcclusionTracker.

We would like to automatically trigger Picture-in-Picture when a certain amount
of the window is occluded. To do this, we need a way to know how much of a
window is occluded by other windows. This occlusion could come from multiple
windows, and an occlusion tracker for aura already exists. This CL extends the
existing occlusion tracking functionality to also track an occluded region for
tracked windows.


Bug: 883157
Bug: 841886
Bug: b/112668686
Bug: b/110011377
Test: unit test
Change-Id: I0d6618ab05109cc46af0cfd72ecc5cbca2f200d4
Reviewed-on: https://chromium-review.googlesource.com/c/1179433
Commit-Queue: Eliot Courtney <edcourtney@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604532}
11 files changed