abstract name of clipping ops, to transtion to a more restricted set

SkRegion::Op --> SkCanvas::ClipOp (alias) --> SkClipOp

pre-CL needed in chrome : https://codereview.chromium.org/2355583002/

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2355483002

Review-Url: https://codereview.chromium.org/2355483002
diff --git a/src/utils/SkNWayCanvas.cpp b/src/utils/SkNWayCanvas.cpp
index 1cd3dc4..e19e7a8 100644
--- a/src/utils/SkNWayCanvas.cpp
+++ b/src/utils/SkNWayCanvas.cpp
@@ -100,7 +100,7 @@
     this->INHERITED::didSetMatrix(matrix);
 }
 
-void SkNWayCanvas::onClipRect(const SkRect& rect, SkRegion::Op op, ClipEdgeStyle edgeStyle) {
+void SkNWayCanvas::onClipRect(const SkRect& rect, ClipOp op, ClipEdgeStyle edgeStyle) {
     Iter iter(fList);
     while (iter.next()) {
         iter->clipRect(rect, op, kSoft_ClipEdgeStyle == edgeStyle);
@@ -108,7 +108,7 @@
     this->INHERITED::onClipRect(rect, op, edgeStyle);
 }
 
-void SkNWayCanvas::onClipRRect(const SkRRect& rrect, SkRegion::Op op, ClipEdgeStyle edgeStyle) {
+void SkNWayCanvas::onClipRRect(const SkRRect& rrect, ClipOp op, ClipEdgeStyle edgeStyle) {
     Iter iter(fList);
     while (iter.next()) {
         iter->clipRRect(rrect, op, kSoft_ClipEdgeStyle == edgeStyle);
@@ -116,7 +116,7 @@
     this->INHERITED::onClipRRect(rrect, op, edgeStyle);
 }
 
-void SkNWayCanvas::onClipPath(const SkPath& path, SkRegion::Op op, ClipEdgeStyle edgeStyle) {
+void SkNWayCanvas::onClipPath(const SkPath& path, ClipOp op, ClipEdgeStyle edgeStyle) {
     Iter iter(fList);
     while (iter.next()) {
         iter->clipPath(path, op, kSoft_ClipEdgeStyle == edgeStyle);
@@ -124,7 +124,7 @@
     this->INHERITED::onClipPath(path, op, edgeStyle);
 }
 
-void SkNWayCanvas::onClipRegion(const SkRegion& deviceRgn, SkRegion::Op op) {
+void SkNWayCanvas::onClipRegion(const SkRegion& deviceRgn, ClipOp op) {
     Iter iter(fList);
     while (iter.next()) {
         iter->clipRegion(deviceRgn, op);