Fix behavior of oneshot accessors of error objects.

src/messages.js

Index: src/messages.js
diff --git a/src/messages.js b/src/messages.js
index 7d0c6bda42f1931e01c787959395caf64cae3b50..81619b32c9019150a7472c4e14c8b30956dc3660 100644
--- a/src/messages.js
+++ b/src/messages.js
@@ -768,23 +768,18 @@ function GetStackTraceLine(recv, fun, pos, isGlobal) {
 
 // Defines accessors for a property that is calculated the first time
 // the property is read.
-function DefineOneShotAccessor(obj, name, fun) {
-  // Note that the accessors consistently operate on 'obj', not 'this'.
-  // Since the object may occur in someone else's prototype chain we
-  // can't rely on 'this' being the same as 'obj'.
-  var value;
-  var value_factory = fun;
+function DefineOneShotAccessor(obj, name, value_factory) {
+  // Note that 'obj' may be different than 'this' since obj may be on the
+  // prototype chain of 'this'.
   var getter = function() {
-    if (value_factory == null) {
-      return value;
-    }
-    value = value_factory(obj);
-    value_factory = null;
+    var value = value_factory(obj);
+    delete obj[name];
+    obj[name] = value;
     return value;
   };
   var setter = function(v) {
-    value_factory = null;
-    value = v;
+    // Set the property for 'this', ignoring this setter.
+    %DefineOrRedefineDataProperty(this, name, v, NONE);
   };
   %DefineOrRedefineAccessorProperty(obj, name, getter, setter, DONT_ENUM);
 }