Move extensibility check to the top of Object.isFrozen/Object.isSealed

This speeds up isFrozen/isSealed checks on "normal" objects without
slowing down checks on frozen/sealed objects.

Though this ordering is not what ES5 specifies, the difference is not
observable (especially since the code bails out if the passed-in object
is a proxy).

Review URL: https://codereview.chromium.org/12340008

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13726 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/v8natives.js

@@ -1246,16 +1246,16 @@ function ObjectIsSealed(obj) {
   if (%IsJSProxy(obj)) {
     return false;
   }
+  if (%IsExtensible(obj)) {
+    return false;
+  }
   var names = ObjectGetOwnPropertyNames(obj);
   for (var i = 0; i < names.length; i++) {
     var name = names[i];
     var desc = GetOwnProperty(obj, name);
     if (desc.isConfigurable()) return false;
   }
-  if (!ObjectIsExtensible(obj)) {
-    return true;
-  }
-  return false;
+  return true;
 }
 
 
@@ -1267,6 +1267,9 @@ function ObjectIsFrozen(obj) {
   if (%IsJSProxy(obj)) {
     return false;
   }
+  if (%IsExtensible(obj)) {
+    return false;
+  }
   var names = ObjectGetOwnPropertyNames(obj);
   for (var i = 0; i < names.length; i++) {
     var name = names[i];
@@ -1274,10 +1277,7 @@ function ObjectIsFrozen(obj) {
     if (IsDataDescriptor(desc) && desc.isWritable()) return false;
     if (desc.isConfigurable()) return false;
   }
-  if (!ObjectIsExtensible(obj)) {
-    return true;
-  }
-  return false;
+  return true;
 }