Implement ToLength from ES6 section 7.1.15

src/runtime.js

Index: src/runtime.js
diff --git a/src/runtime.js b/src/runtime.js
index d9e1fe5c994030f40461167faac8b3df4d60ff22..4d15d205a495b6623cf399ccd0dd36973cac22c4 100644
--- a/src/runtime.js
+++ b/src/runtime.js
@@ -563,6 +563,14 @@ function ToInteger(x) {
 }
 
 
+// ES6, draft 08-24-14, section 7.1.15
+function ToLength(arg) {
+  arg = ToInteger(arg);
+  if (arg < 0) return 0;
+  return arg < $Number.MAX_SAFE_INTEGER ? arg : $Number.MAX_SAFE_INTEGER;
+}
+
+
 // ECMA-262, section 9.6, page 34.
 function ToUint32(x) {
   if (%_IsSmi(x) && x >= 0) return x;