bug:27225580
bug:27281241
Empty unclipped savelayers (clipped at defer time, often by dirty rect)
were resulting in invalid layer clear rectangles. Simplify by just
rejecting these unclipped savelayers entirely at defer.
Also, use repaint rect as base clip for constructed ops within
LayerBuilder.
Change-Id: I5c466199e85201a2f68f5cdc60b29187c849961b
Can't safely rewind clip allocations, since those pointers are cached by
ClipArea. Instead add early rejection to handle most cases, and update
tests.
Change-Id: Ic32f95cf95602f427f25761a8da1583c4495f36d
