Add additive animation support for CSS property clip

third_party/WebKit/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 830 matching lines @@
             'animation/AnimationEffect.cpp',
             'animation/AnimationEffect.h',
             'animation/AnimationEffectTiming.cpp',
             'animation/AnimationEffectTiming.h',
             'animation/Animation.cpp',
             'animation/Animation.h',
             'animation/AnimationStack.cpp',
             'animation/AnimationStack.h',
             'animation/AnimationTimeline.cpp',
             'animation/AnimationTimeline.h',
+            'animation/CSSClipInterpolationType.cpp',
+            'animation/CSSClipInterpolationType.h',
             'animation/CSSColorInterpolationType.cpp',
             'animation/CSSColorInterpolationType.h',
             'animation/CSSFontWeightInterpolationType.cpp',
             'animation/CSSFontWeightInterpolationType.h',
             'animation/CSSImageInterpolationType.cpp',
             'animation/CSSImageInterpolationType.h',
             'animation/CSSImageListInterpolationType.cpp',
             'animation/CSSImageListInterpolationType.h',
             'animation/CSSInterpolationType.cpp',
             'animation/CSSInterpolationType.h',
@@ skipping 3154 matching lines @@
             'style/SVGComputedStyleTest.cpp',
             'svg/SVGPathParserTest.cpp',
             'svg/UnsafeSVGAttributeSanitizationTest.cpp',
             'testing/PrivateScriptTestTest.cpp',
             'timing/MemoryInfoTest.cpp',
             'workers/WorkerThreadTest.cpp',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }