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

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2357333002

Review-Url: https://codereview.chromium.org/2357333002
diff --git a/gm/distantclip.cpp b/gm/distantclip.cpp
index f4931dd..24fbaca 100644
--- a/gm/distantclip.cpp
+++ b/gm/distantclip.cpp
@@ -39,7 +39,7 @@
         SkRect r = SkRect::MakeXYWH(-kExtents, kOffset - kExtents, 2 * kExtents, 2 * kExtents);
         SkPath p;
         p.addRoundRect(r, 5, 5);
-        rec->clipPath(p, SkCanvas::kIntersect_Op, true);
+        rec->clipPath(p, true);
         rec->drawColor(SK_ColorGREEN);
         rec->restore();
         sk_sp<SkPicture> pict(recorder.finishRecordingAsPicture());