[turbofan] First step towards sanitizing for-in and making it optimizable.

src/runtime.js

Index: src/runtime.js
diff --git a/src/runtime.js b/src/runtime.js
index d1ebc301fbdbf3c42e70f60fc23900b79d531033..b6007789c4332fec8f7d92a7ab20671a0573f927 100644
--- a/src/runtime.js
+++ b/src/runtime.js
@@ -49,7 +49,6 @@ var SHR_STRONG;
 var DELETE;
 var IN;
 var INSTANCE_OF;
-var FILTER_KEY;
 var CALL_NON_FUNCTION;
 var CALL_NON_FUNCTION_AS_CONSTRUCTOR;
 var CALL_FUNCTION_PROXY;
@@ -561,16 +560,6 @@ INSTANCE_OF = function INSTANCE_OF(F) {
 }
 
 
-// Filter a given key against an object by checking if the object
-// has a property with the given key; return the key as a string if
-// it has. Otherwise returns 0 (smi). Used in for-in statements.
-FILTER_KEY = function FILTER_KEY(key) {
-  var string = %$toName(key);
-  if (%HasProperty(this, string)) return string;
-  return 0;
-}
-
-
 CALL_NON_FUNCTION = function CALL_NON_FUNCTION() {
   var delegate = %GetFunctionDelegate(this);
   if (!IS_FUNCTION(delegate)) {