Remove PostAttachCallbacks and replace with something more specialized

Source/core/core.gypi

 {
     'variables': {
         # Files for which bindings (.cpp and .h files) will be generated
         'core_idl_files': [
             'animation/Animation.idl',
             'animation/AnimationPlayer.idl',
             'animation/TimedItem.idl',
             'animation/Timeline.idl',
             'animation/Timing.idl',
             'clipboard/DataTransfer.idl',
@@ skipping 1998 matching lines @@
             'dom/NodeRenderStyle.h',
             'dom/NodeTraversal.cpp',
             'dom/NodeTraversal.h',
             'dom/NodeWithIndex.h',
             'dom/Notation.h',
             'dom/ParentNode.h',
             'dom/PendingScript.cpp',
             'dom/Position.cpp',
             'dom/PositionIterator.cpp',
             'dom/PositionIterator.h',
-            'dom/PostAttachCallbacks.cpp',
-            'dom/PostAttachCallbacks.h',
             'dom/PresentationAttributeStyle.cpp',
             'dom/PresentationAttributeStyle.h',
             'dom/ProcessingInstruction.cpp',
             'dom/ProcessingInstruction.h',
             'dom/Promise.h',
             'dom/PseudoElement.cpp',
             'dom/QualifiedName.cpp',
             'dom/Range.cpp',
             'dom/RawDataDocumentParser.h',
             'dom/RequestAnimationFrameCallback.h',
@@ skipping 1294 matching lines @@
             'html/track/vtt/BufferedLineReaderTest.cpp',
             'html/track/vtt/VTTScannerTest.cpp',
             'rendering/RenderOverflowTest.cpp',
             'rendering/shapes/BoxShapeTest.cpp',
             'testing/UnitTestHelpers.cpp',
             'testing/UnitTestHelpers.h',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }