Web Animations: Split image slice interpolation out of LengthBoxStyleInterpolation

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/AnimationNode.idl',
@@ skipping 881 matching lines @@
             'animation/DocumentAnimation.h',
             'animation/DocumentAnimations.cpp',
             'animation/DocumentAnimations.h',
             'animation/DoubleStyleInterpolation.h',
             'animation/DoubleStyleInterpolation.cpp',
             'animation/EffectInput.cpp',
             'animation/EffectInput.h',
             'animation/ElementAnimation.h',
             'animation/ElementAnimations.cpp',
             'animation/ElementAnimations.h',
+            'animation/ImageSliceStyleInterpolation.cpp',
+            'animation/ImageSliceStyleInterpolation.h',
             'animation/ImageStyleInterpolation.cpp',
             'animation/ImageStyleInterpolation.h',
             'animation/InertAnimation.cpp',
             'animation/InertAnimation.h',
             'animation/InterpolableValue.cpp',
             'animation/InterpolableValue.h',
             'animation/Interpolation.cpp',
             'animation/Interpolation.h',
             'animation/InterpolationEffect.cpp',
             'animation/InterpolationEffect.h',
@@ skipping 2899 matching lines @@
             'paint/ViewDisplayListTest.cpp',
             'streams/ExclusiveStreamReaderTest.cpp',
             'streams/ReadableStreamTest.cpp',
             'testing/PrivateScriptTestTest.cpp',
             'testing/UnitTestHelpers.cpp',
             'testing/UnitTestHelpers.h',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }