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

gm/imagefilters.cpp

Index: gm/imagefilters.cpp
diff --git a/gm/imagefilters.cpp b/gm/imagefilters.cpp
index 3e8d39a8792576d4ee657d145f1a616c60f92510..e9f54a312d8ea3592112abba37a2f86bbb0f9f5f 100644
--- a/gm/imagefilters.cpp
+++ b/gm/imagefilters.cpp
@@ -122,7 +122,7 @@ static void draw_set(SkCanvas* canvas, sk_sp<SkImageFilter> filters[], int count
     for (int i = 0; i < count; ++i) {
         canvas->save();
         SkRRect rr = SkRRect::MakeRectXY(r.makeOffset(dx, dy), 20, 20);
-        canvas->clipRRect(rr, SkCanvas::kIntersect_Op, true);
+        canvas->clipRRect(rr, true);
         canvas->saveLayer({ &rr.getBounds(), nullptr, filters[i].get(), 0 });
         canvas->drawColor(0x40FFFFFF);
         canvas->restore();