Update clearOp for split-OpList world

It would reduce a lot of noise if the GrRenderTargetOpList kept a pointer to the GrCaps but, for now, I'm trying to shrink the GrRTOpList, not expand it.

Change-Id: Ieed56fa2a41a3fb20234e26552ae2d301147e4f2
Reviewed-on: https://skia-review.googlesource.com/17323
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
4 files changed