allow clip calls w/o op param, remove unnecessary kReplace ops

gm/pathopsskpclip.cpp

Index: gm/pathopsskpclip.cpp
diff --git a/gm/pathopsskpclip.cpp b/gm/pathopsskpclip.cpp
index 77ba84c73c058814255c9f4802242dc526d1d364..18be6815799cce254d59be00b2213dfd1e4edd29 100644
--- a/gm/pathopsskpclip.cpp
+++ b/gm/pathopsskpclip.cpp
@@ -42,9 +42,9 @@ protected:
             SkIntToScalar(700)
         };
         p.addRoundRect(r, SkIntToScalar(50), SkIntToScalar(50));
-        rec->clipPath(p, SkCanvas::kIntersect_Op, true);
+        rec->clipPath(p, true);
         rec->translate(SkIntToScalar(250), SkIntToScalar(250));
-        rec->clipPath(p, SkCanvas::kIntersect_Op, true);
+        rec->clipPath(p, true);
         rec->drawColor(0xffff0000);
         sk_sp<SkPicture> pict(recorder.finishRecordingAsPicture());