Revert of Overlays: Remove special casing of primary overlay plane

Revert of Overlays: Remove special casing of primary overlay plane (patchset #5 id:80001 of https://codereview.chromium.org/1376883004/ )

Reason for revert:
Speculative revert because this might be related to a browser crash rate uptick in crbug.com/539374.

Original issue's description:
> Overlays: Remove special casing of primary overlay plane
> 
> Mac will soon want to skip drawing the primary overlay plane, which
> now can be accomplished by having the overlay strategy simply not emit
> it.
> 
> BUG=533687
> CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
> 
> Committed: https://crrev.com/e532ed0710935ef66a860b08b8e2a1e36a426b27
> Cr-Commit-Position: refs/heads/master@{#352186}

TBR=alexst@chromium.org,dnicoara@chromium.org,achaulk@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=533687

[ccameron, 2015-10-05 17:47:19]

Created Revert of Overlays: Remove special casing of primary overlay plane

[ccameron, 2015-10-05 17:48:06]

The CQ bit was unchecked by ccameron@chromium.org