Slightly optimize performance of ToLength()

src/runtime.js

Index: src/runtime.js
diff --git a/src/runtime.js b/src/runtime.js
index 39939b16027f9447967becf4e3b374aafdb8fd21..c41c4d91ddeb85e5cf7eec5aa83a4b55a380a246 100644
--- a/src/runtime.js
+++ b/src/runtime.js
@@ -300,10 +300,11 @@ function ToInteger(x) {
 
 // ES6, draft 08-24-14, section 7.1.15
 function ToLength(arg) {
-  arg = ToInteger(arg);
+  if (!%_IsSmi(arg)) {
+    arg = %NumberToInteger(ToNumber(arg));
+  }
   if (arg < 0) return 0;
-  return arg < GlobalNumber.MAX_SAFE_INTEGER ? arg
-                                             : GlobalNumber.MAX_SAFE_INTEGER;
+  return arg < kMaxSafeInteger ? arg : kMaxSafeInteger;
 }