cc: Always call PrepareTiles on visibility change.
cc: Always call PrepareTiles on visibility change.

When using SingleThreadProxy with impl side painting the scheduler waits
for the READY_TO_DRAW signal indefinitely. If renderer switches from
visible to invisible and back again it gets in a state where it won't
ever call PrepareTiles and not advance frames indefinitely. Calling
PrepareTiles unconditionally on visiblity changes fixes that.

BUG=497473
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1169213002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#333576}

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