Fix issue 720 making Object.defineProperty handle existing writable flags cor...

src/v8natives.js

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 586 matching lines @@
   }
 
   if (desc.hasConfigurable()) {
     flag |= desc.isConfigurable() ? 0 : DONT_DELETE;
   } else if (!IS_UNDEFINED(current)) {
     flag |= current.isConfigurable() ? 0 : DONT_DELETE;
   } else
     flag |= DONT_DELETE;
 
   if (IsDataDescriptor(desc) || IsGenericDescriptor(desc)) {
-    flag |= desc.isWritable() ? 0 : READ_ONLY;
+    if (desc.hasWritable()) {
+      flag |= desc.isWritable() ? 0 : READ_ONLY;
+    } else if (!IS_UNDEFINED(current)) {
+      flag |= current.isWritable() ? 0 : READ_ONLY;
+    } else {
+      flag |= READ_ONLY;
+    }
     %DefineOrRedefineDataProperty(obj, p, desc.getValue(), flag);
   } else {
     if (desc.hasGetter() && IS_FUNCTION(desc.getGet())) {
        %DefineOrRedefineAccessorProperty(obj, p, GETTER, desc.getGet(), flag);
     }
     if (desc.hasSetter() && IS_FUNCTION(desc.getSet())) {
       %DefineOrRedefineAccessorProperty(obj, p, SETTER, desc.getSet(), flag);
     }
   }
   return true;
@@ skipping 406 matching lines @@
 
 // ----------------------------------------------------------------------------
 
 function SetupFunction() {
   InstallFunctions($Function.prototype, DONT_ENUM, $Array(
     "toString", FunctionToString
   ));
 }
 
 SetupFunction();