Faster invocation of custom comparator function.

src/x64/codegen-x64.h

Index: src/x64/codegen-x64.h
diff --git a/src/x64/codegen-x64.h b/src/x64/codegen-x64.h
index 35e1f4439ab724b6135eadc3335be7110bae7dcd..081a8a83719b81dd7fbc9b7cf5288e8db897dfbb 100644
--- a/src/x64/codegen-x64.h
+++ b/src/x64/codegen-x64.h
@@ -585,6 +585,9 @@ class CodeGenerator: public AstVisitor {
   // Fast support for number to string.
   void GenerateNumberToString(ZoneList<Expression*>* args);
 
+  // Fast call for custom callbacks.
+  void GenerateCallFunction(ZoneList<Expression*>* args);
+
   // Fast call to math functions.
   void GenerateMathPow(ZoneList<Expression*>* args);
   void GenerateMathSin(ZoneList<Expression*>* args);