Have DOMImplementation::document() return reference.

Source/bindings/tests/idls/TestInterfacePython4.idl

Index: Source/bindings/tests/idls/TestInterfacePython4.idl
diff --git a/Source/bindings/tests/idls/TestInterfacePython4.idl b/Source/bindings/tests/idls/TestInterfacePython4.idl
new file mode 100644
index 0000000000000000000000000000000000000000..0b1a514aa5d25ab9a523a2d7d9bdc2573f8001cb
--- /dev/null
+++ b/Source/bindings/tests/idls/TestInterfacePython4.idl
@@ -0,0 +1,12 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// This is for interface extended attributes that interact with another extended
+// attribute, and thus both cannot be tested at once.
+// The more *minor* extended attribute should be put in this file.
+
+[
+    SetWrapperReferenceFromReference=document,  // Conflicts with [SetWrapperReferenceTo], [SetWrapperReferenceFrom] and [Custom=VisitDOMWrapper]
+] interface TestInterfacePython4 {   
+};