Convert GrClip to an abstract base class

include/gpu/GrTypesPriv.h

Index: include/gpu/GrTypesPriv.h
diff --git a/include/gpu/GrTypesPriv.h b/include/gpu/GrTypesPriv.h
index 18bc6449aad110f0f51a450d9cb26fd44413bebc..154a107e0da13602a49d5878f77473c242d7309b 100644
--- a/include/gpu/GrTypesPriv.h
+++ b/include/gpu/GrTypesPriv.h
@@ -401,7 +401,10 @@ enum GrIOType {
 
 struct GrScissorState {
     GrScissorState() : fEnabled(false) {}
+    GrScissorState(const SkIRect& rect) : fEnabled(true), fRect(rect) {}
+    void setDisabled() { fEnabled = false; }
     void set(const SkIRect& rect) { fRect = rect; fEnabled = true; }
+    void setNonAA(const SkRect& rect) { rect.round(&fRect); fEnabled = true; }
     bool operator==(const GrScissorState& other) const {
         return fEnabled == other.fEnabled &&
                 (false == fEnabled || fRect == other.fRect);