Make sure the rootNode of a LiveNodeListBase is always a ContainerNode

Source/core/core.gypi

 {
     'variables': {
         # Files for which bindings (.cpp and .h files) will be generated
         'core_idl_files': [
             'animation/Animation.idl',
             'animation/Player.idl',
             'animation/TimedItem.idl',
             'css/CSS.idl',
             'css/CSSCharsetRule.idl',
             'css/CSSFontFaceLoadEvent.idl',
@@ skipping 1911 matching lines @@
             'dom/DOMURLUtils.h',
             'dom/DOMURLUtilsReadOnly.cpp',
             'dom/DOMURLUtilsReadOnly.h',
             'dom/Element.cpp',
             'dom/Element.h',
             'dom/ElementData.cpp',
             'dom/ElementData.h',
             'dom/ElementRareData.cpp',
             'dom/ElementRareData.h',
             'dom/ElementTraversal.h',
+            'dom/EmptyNodeList.cpp',
+            'dom/EmptyNodeList.h',
             'dom/Entity.h',
             'dom/ExecutionContextTask.cpp',
             'dom/ExecutionContextTask.h',
             'dom/MainThreadTaskRunner.cpp',
             'dom/MainThreadTaskRunner.h',
             'dom/FullscreenElementStack.cpp',
             'dom/FullscreenElementStack.h',
             'dom/GlobalEventHandlers.h',
             'dom/IconURL.cpp',
             'dom/IconURL.h',
@@ skipping 1326 matching lines @@
             'html/track/vtt/BufferedLineReaderTest.cpp',
             'html/track/vtt/VTTScannerTest.cpp',
             'frame/ImageBitmapTest.cpp',
             'rendering/RenderOverflowTest.cpp',
             'rendering/shapes/BoxShapeTest.cpp',
             'testing/UnitTestHelpers.h',
             'testing/UnitTestHelpers.cpp',
         ],
     }
 }