change SkClipOp to a class enum

BUG=skia:

Change-Id: I25dbe6d6b8666a2a0a7be7bdd2ae0b067868d14e
Reviewed-on: https://skia-review.googlesource.com/5718
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/gm/gm.h b/gm/gm.h
index ff033a8..0b26c16 100644
--- a/gm/gm.h
+++ b/gm/gm.h
@@ -15,6 +15,7 @@
 #include "SkString.h"
 #include "SkTRegistry.h"
 #include "sk_tool_utils.h"
+#include "SkClipOpPriv.h"
 
 class SkAnimTimer;
 struct GrContextOptions;