Introduce ES6 iterator for DOM objects.

Source/core/core.gypi

 {
     'includes': [
       'core_generated.gypi',
     ],
     'variables': {
         # Files for which bindings (.cpp and .h files) will be generated
         'core_idl_files': [
             'animation/Animation.idl',
             'animation/AnimationEffect.idl',
             'animation/AnimationPlayer.idl',
@@ skipping 54 matching lines @@
             'dom/DOMRect.idl',
             'dom/DOMRectReadOnly.idl',
             'dom/DOMSettableTokenList.idl',
             'dom/DOMStringList.idl',
             'dom/DOMStringMap.idl',
             'dom/DOMTokenList.idl',
             'dom/Document.idl',
             'dom/DocumentFragment.idl',
             'dom/DocumentType.idl',
             'dom/Element.idl',
+            'dom/Iterator.idl',
             'dom/MessageChannel.idl',
             'dom/MessagePort.idl',
             'dom/MutationObserver.idl',
             'dom/MutationRecord.idl',
             'dom/NamedNodeMap.idl',
             'dom/Node.idl',
             'dom/NodeFilter.idl',
             'dom/NodeIterator.idl',
             'dom/NodeList.idl',
             'dom/ProcessingInstruction.idl',
@@ skipping 1949 matching lines @@
             'dom/GlobalEventHandlers.h',
             'dom/IconURL.cpp',
             'dom/IconURL.h',
             'dom/IdTargetObserver.cpp',
             'dom/IdTargetObserver.h',
             'dom/IdTargetObserverRegistry.cpp',
             'dom/IdTargetObserverRegistry.h',
             'dom/IgnoreDestructiveWriteCountIncrementer.h',
             'dom/IncrementLoadEventDelayCount.cpp',
             'dom/IncrementLoadEventDelayCount.h',
+            'dom/Iterator.h',
             'dom/LiveNodeList.cpp',
             'dom/LiveNodeList.h',
             'dom/LiveNodeListBase.cpp',
             'dom/LiveNodeListBase.h',
             'dom/MainThreadTaskRunner.cpp',
             'dom/MainThreadTaskRunner.h',
             'dom/MessageChannel.cpp',
             'dom/MessageChannel.h',
             'dom/MessagePort.cpp',
             'dom/Microtask.cpp',
@@ skipping 1412 matching lines @@
             'rendering/shapes/BoxShapeTest.cpp',
             'rendering/style/OutlineValueTest.cpp',
             'testing/PrivateScriptTestTest.cpp',
             'streams/ReadableStreamTest.cpp',
             'testing/UnitTestHelpers.cpp',
             'testing/UnitTestHelpers.h',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }