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This patch ensures that we always activate when we become invisible.
The reason being is that when we come back to being visible again,
we don't need to rasterize both active and pending trees. We can
just rasterize what used to be the pending tree.

Since we set RequiresHighResToDraw on becoming visible, this also
ensures that we don't checkerboard on becoming visible.

BUG=410000, 417598
R=danakj, enne, brianderson

Review URL: https://codereview.chromium.org/605823002

Cr-Commit-Position: refs/heads/master@{#297303}