Add template parameter to ElementTraversal to iterate over Elements of a specific type

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',
             'animation/Timeline.idl',
             'animation/Timing.idl',
             'clipboard/Clipboard.idl',
@@ skipping 1944 matching lines @@
             'dom/NameNodeList.h',
             'dom/Node.cpp',
             'dom/NodeChildRemovalTracker.h',
             'dom/NodeChildRemovalTracker.cpp',
             'dom/NodeFilter.cpp',
             'dom/NodeFilter.h',
             'dom/NodeFilterCondition.cpp',
             'dom/NodeFilterCondition.h',
             'dom/NodeIterator.cpp',
             'dom/NodeIterator.h',
+            'dom/NodeIteratorBase.cpp',
+            'dom/NodeIteratorBase.h',
             'dom/NodeRareData.cpp',
             'dom/NodeRareData.h',
             'dom/RenderTreeBuilder.cpp',
             'dom/RenderTreeBuilder.h',
             'dom/NodeRenderingTraversal.cpp',
             'dom/NodeRenderingTraversal.h',
             'dom/NodeRenderStyle.h',
             'dom/NodeTraversal.cpp',
             'dom/NodeTraversal.h',
             'dom/NodeWithIndex.h',
@@ skipping 101 matching lines @@
             'dom/TagCollection.h',
             'dom/Text.cpp',
             'dom/TextLinkColors.cpp',
             'dom/TextLinkColors.h',
             'dom/Touch.cpp',
             'dom/Touch.h',
             'dom/TouchList.cpp',
             'dom/TouchList.h',
             'dom/TransformSource.h',
             'dom/TransformSourceLibxslt.cpp',
-            'dom/Traversal.cpp',
-            'dom/Traversal.h',
             'dom/TreeScope.cpp',
             'dom/TreeScope.h',
             'dom/TreeScopeAdopter.cpp',
             'dom/TreeScopeAdopter.h',
             'dom/TreeScopeStyleSheetCollection.cpp',
             'dom/TreeScopeStyleSheetCollection.h',
             'dom/TreeShared.h',
             'dom/TreeWalker.cpp',
             'dom/TreeWalker.h',
             'dom/UserActionElementSet.cpp',
@@ skipping 1185 matching lines @@
             'html/parser/HTMLParserThreadTest.cpp',
             'html/track/vtt/BufferedLineReaderTest.cpp',
             'html/track/vtt/VTTScannerTest.cpp',
             'rendering/RenderOverflowTest.cpp',
             'rendering/shapes/BoxShapeTest.cpp',
             'testing/UnitTestHelpers.cpp',
             'testing/UnitTestHelpers.h',
         ],
     }
 }