Add workaround for redefinition of __proto__ property.

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index e914a3ae3291ee411b2c3a80122b2725c507fd90..52a0a7b3c7139051f384eb2beef1ebe620f13e05 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -4091,6 +4091,13 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_DefineOrRedefineDataProperty) {
     if (callback->IsAccessorInfo()) {
       return isolate->heap()->undefined_value();
     }
+    // TODO(mstarzinger): The __proto__ property should actually be a real
+    // JavaScript accessor instead of a foreign callback. But for now we just
+    // avoid changing the writability attribute of this property.
+    Handle<String> proto_string = isolate->factory()->proto_string();
+    if (callback->IsForeign() && proto_string->Equals(*name)) {
+      attr = static_cast<PropertyAttributes>(attr & ~READ_ONLY);

[rossberg, 2013/03/04 16:04:42]

As discussed offline, this should also filter DONT_DELETE. More importantly,
DONT_DELETE should be false initially.

[Michael Starzinger, 2013/03/04 16:24:58]

Done.

+    }
     // Avoid redefining foreign callback as data property, just use the stored
     // setter to update the value instead.
     // TODO(mstarzinger): So far this only works if property attributes don't