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This CL adds a new state to ScenicWindow that checks if the view
is attached to a rendered scene graph.

Bug: 1044802
Change-Id: Ieeb98a2bbe4d214fed302d60360dd77f0b702838
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2015675
Commit-Queue: Emircan Uysaler <emircan@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#741155}