Expose scroll customization for touch to JS (behind REF).

Source/core/core.gypi

 {
     'includes': [
         'core_generated.gypi',
     ],
     'variables': {
         # Files for which bindings (.cpp and .h files) will be generated
         'core_idl_files': [
             'animation/KeyframeEffect.idl',
             'animation/EffectModel.idl',
             'animation/AnimationEffectReadOnly.idl',
@@ skipping 272 matching lines @@
             'html/track/VideoTrackList.idl',
             'html/track/vtt/VTTCue.idl',
             'html/track/vtt/VTTRegion.idl',
             'html/track/vtt/VTTRegionList.idl',
             'input/InputDevice.idl',
             'inspector/InspectorOverlayHost.idl',
             'loader/appcache/ApplicationCache.idl',
             'page/EventSource.idl',
             'page/PagePopupController.idl',
             'page/scrolling/ScrollState.idl',
+             'page/scrolling/ScrollStateCallback.idl',
             'streams/ReadableByteStream.idl',
             'streams/ReadableByteStreamReader.idl',
             'streams/ReadableStream.idl',
             'streams/ReadableStreamReader.idl',
             'streams/Stream.idl',
             'svg/SVGAElement.idl',
             'svg/SVGAngle.idl',
             'svg/SVGAnimateElement.idl',
             'svg/SVGAnimateMotionElement.idl',
             'svg/SVGAnimateTransformElement.idl',
@@ skipping 1526 matching lines @@
             'page/TouchAdjustment.h',
             'page/TouchDisambiguation.cpp',
             'page/TouchDisambiguation.h',
             'page/WindowFeatures.cpp',
             'page/scrolling/ScrollingConstraints.cpp',
             'page/scrolling/ScrollingConstraints.h',
             'page/scrolling/ScrollingCoordinator.cpp',
             'page/scrolling/ScrollingCoordinator.h',
             'page/scrolling/ScrollState.cpp',
             'page/scrolling/ScrollState.h',
+            'page/scrolling/ScrollStateCallback.cpp',
+            'page/scrolling/ScrollStateCallback.h',
             'paint/BackgroundImageGeometry.cpp',
             'paint/BackgroundImageGeometry.h',
             'paint/BlockFlowPainter.cpp',
             'paint/BlockFlowPainter.h',
             'paint/BlockPainter.cpp',
             'paint/BlockPainter.h',
             'paint/BoxBorderPainter.cpp',
             'paint/BoxBorderPainter.h',
             'paint/BoxClipper.cpp',
             'paint/BoxClipper.h',
@@ skipping 2104 matching lines @@
             'style/OutlineValueTest.cpp',
             'style/SVGComputedStyleTest.cpp',
             'svg/UnsafeSVGAttributeSanitizationTest.cpp',
             'testing/PrivateScriptTestTest.cpp',
             'timing/MemoryInfoTest.cpp',
             'workers/WorkerThreadTest.cpp',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }