cc: Use occlusion for deciding raster/eviction priorities in browser

cc: Use occlusion for deciding raster/eviction priorities in browser

The browser compositor should use occlusion to allow lots of
overlapping windows to take up less memory. This reduces our memory
consumption in ash a bit.

Though, the window UI is not considered opaque currently, so more
memory is still used than could be otherwise.

R=enne, vmpstr
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Committed: https://crrev.com/0006e95b207be0bca6a8e6850e2d1f5147b453e4
Cr-Commit-Position: refs/heads/master@{#342493}

[danakj, 2015-08-07 22:02:13]

ping

[vmpstr, 2015-08-07 22:06:33]

lgtm

[danakj, 2015-08-07 22:07:02]

The CQ bit was checked by danakj@chromium.org

[commit-bot: I haz the power, 2015-08-07 22:07:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1277053002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1277053002/1

[commit-bot: I haz the power, 2015-08-08 00:37:02]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-08 00:38:13]

Patchset 1 (id:??) landed as
https://crrev.com/0006e95b207be0bca6a8e6850e2d1f5147b453e4
Cr-Commit-Position: refs/heads/master@{#342493}