Add back [ImplementedInBaseClass] IDL extended attribute

Source/bindings/tests/idls/TestImplements3.idl

Index: Source/bindings/tests/idls/TestImplements3.idl
diff --git a/Source/bindings/tests/idls/TestImplements3.idl b/Source/bindings/tests/idls/TestImplements3.idl
new file mode 100644
index 0000000000000000000000000000000000000000..e5e13a4ae0d05396526399533a778e624ad9bdf6
--- /dev/null
+++ b/Source/bindings/tests/idls/TestImplements3.idl
@@ -0,0 +1,13 @@
+// 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.
+
+[
+    ImplementedInBaseClass, // Conflicts with default implements class name and [ImplementedAs]
+    NoInterfaceObject,
+] interface TestImplements3 {
+    attribute DOMString implements3StringAttribute;
+    static attribute DOMString implements3StaticStringAttribute;
+    void implements3VoidMethod();
+    static void implements3StaticVoidMethod();
+};