Inline %_ArgumentsLength.

src/x64/macro-assembler-x64.cc

Index: src/x64/macro-assembler-x64.cc
diff --git a/src/x64/macro-assembler-x64.cc b/src/x64/macro-assembler-x64.cc
index a8e2fdfea4d6967db515dc702ffac7f9f2769837..2781a8489885e43e72a572b29a4efda3a5c4272f 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -1660,6 +1660,15 @@ void MacroAssembler::AbortIfNotNumber(Register object, const char* msg) {
 }
 
 
+void MacroAssembler::AbortIfNotSmi(Register object, const char* msg) {
+  Label ok;
+  Condition is_smi = CheckSmi(object);
+  j(is_smi, &ok);
+  Assert(equal, msg);
+  bind(&ok);
+}
+
+
 Condition MacroAssembler::IsObjectStringType(Register heap_object,
                                              Register map,
                                              Register instance_type) {