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/tests/SkLiteDLTest.cpp b/tests/SkLiteDLTest.cpp
index 70a9077..f3fccc8 100644
--- a/tests/SkLiteDLTest.cpp
+++ b/tests/SkLiteDLTest.cpp
@@ -13,7 +13,7 @@
     sk_sp<SkLiteDL> p { SkLiteDL::New({2,2,3,3}) };
 
     p->save();
-        p->clipRect(SkRect{2,3,4,5}, SkRegion::kIntersect_Op, true);
+        p->clipRect(SkRect{2,3,4,5}, SkCanvas::kIntersect_Op, true);
         p->drawRect(SkRect{0,0,9,9}, SkPaint{});
     p->restore();
 }
@@ -27,7 +27,7 @@
     rec.reset(p.get());
 
     c->save();
-        c->clipRect(SkRect{2,3,4,5}, SkRegion::kIntersect_Op, true);
+        c->clipRect(SkRect{2,3,4,5}, SkCanvas::kIntersect_Op, true);
         c->drawRect(SkRect{0,0,9,9}, SkPaint{});
     c->restore();
 }