added support for sk_ClipDistance

Change-Id: I9ea202679211b98cf98165c8609f24f9b4e14b66
Reviewed-on: https://skia-review.googlesource.com/8247
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
diff --git a/src/sksl/SkSLCompiler.h b/src/sksl/SkSLCompiler.h
index 167f042..f7dcf2b 100644
--- a/src/sksl/SkSLCompiler.h
+++ b/src/sksl/SkSLCompiler.h
@@ -17,9 +17,10 @@
 #include "SkSLErrorReporter.h"
 #include "SkSLIRGenerator.h"
 
-#define SK_FRAGCOLOR_BUILTIN 10001
-#define SK_FRAGCOORD_BUILTIN    15
-#define SK_VERTEXID_BUILTIN      5
+#define SK_FRAGCOLOR_BUILTIN    10001
+#define SK_FRAGCOORD_BUILTIN       15
+#define SK_VERTEXID_BUILTIN         5
+#define SK_CLIPDISTANCE_BUILTIN     3
 
 namespace SkSL {