Add support for DOM4's XMLDocument interface

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 70 matching lines @@
             'dom/Range.idl',
             'dom/RequestAnimationFrameCallback.idl',
             'dom/StringCallback.idl',
             'dom/Text.idl',
             'dom/Touch.idl',
             'dom/TouchList.idl',
             'dom/TreeWalker.idl',
             'dom/URL.idl',
             'dom/WebKitNamedFlow.idl',
             'dom/WebKitNamedFlowCollection.idl',
+            'dom/XMLDocument.idl',
             'dom/shadow/ShadowRoot.idl',
             'events/AutocompleteErrorEvent.idl',
             'events/BeforeLoadEvent.idl',
             'events/BeforeUnloadEvent.idl',
             'events/CompositionEvent.idl',
             'events/CustomEvent.idl',
             'events/ErrorEvent.idl',
             'events/Event.idl',
             'events/EventTarget.idl',
             'events/FocusEvent.idl',
@@ skipping 1916 matching lines @@
             'dom/ScriptedAnimationController.cpp',
             'dom/ScriptedAnimationController.h',
             'dom/ExecutionContext.cpp',
             'dom/ScriptLoader.cpp',
             'dom/ScriptLoader.h',
             'dom/ScriptRunner.cpp',
             'dom/SecurityContext.cpp',
             'dom/SecurityContext.h',
             'dom/SelectorQuery.cpp',
             'dom/SelectorQuery.h',
+            'dom/XMLDocument.cpp',
+            'dom/XMLDocument.h',
             'dom/custom/CustomElement.cpp',
             'dom/custom/CustomElement.h',
             'dom/custom/CustomElementCallbackDispatcher.cpp',
             'dom/custom/CustomElementCallbackDispatcher.h',
             'dom/custom/CustomElementCallbackInvocation.cpp',
             'dom/custom/CustomElementCallbackInvocation.h',
             'dom/custom/CustomElementCallbackQueue.cpp',
             'dom/custom/CustomElementCallbackQueue.h',
             'dom/custom/CustomElementDefinition.cpp',
             'dom/custom/CustomElementDefinition.h',
@@ skipping 1230 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',
         ],
     }
 }