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/SkLua.cpp b/src/utils/SkLua.cpp
index 117cb8a..d9beaed 100644
--- a/src/utils/SkLua.cpp
+++ b/src/utils/SkLua.cpp
@@ -405,7 +405,7 @@
             this->pushPath(element.getPath(), "path");
             break;
     }
-    this->pushString(region_op(element.getOp()), "op");
+    this->pushString(region_op((SkRegion::Op)element.getOp()), "op");
     this->pushBool(element.isAA(), "aa");
     CHECK_SETFIELD(key);
 }