Implement Array.from()

src/runtime.js

Index: src/runtime.js
diff --git a/src/runtime.js b/src/runtime.js
index d9e1fe5c994030f40461167faac8b3df4d60ff22..d49b6d267dd2c93d69daaca86caa07282b268bf6 100644
--- a/src/runtime.js
+++ b/src/runtime.js
@@ -465,6 +465,16 @@ function TO_STRING() {
 }
 
 
+// ES6, draft 07-18-14, section 7.1.15
+function TO_LENGTH(arg) {
+  arg = ToInteger(arg);
+  if (arg < +0) {
+    return 0;
+  }
+  return arg < $Number.MAX_SAFE_INTEGER ? arg : $Number.MAX_SAFE_INTEGER;
+}
+
+
 /* -------------------------------------
    - - -   C o n v e r s i o n s   - - -
    -------------------------------------