Only use scissor state for native clears

This is the first of many CLs that progressively refine the clipping,
scissoring, and clearing APIs.

The series of changes focus on simplifying the clear APIs, consolidating
clip intersection logic, and moving towards a more explicitly sized
render target context (where confusion between approx-fit and exact-fit
is handled externally, although I don't take it that far).

Next step will be to propagate the simpler calls up to GrRTC.

Change-Id: Idb0c58a63b7a3950a92604dd4c03536d668be7c4
Commit-Queue: Michael Ludwig <>
Reviewed-by: Chris Dalton <>
24 files changed