Support mask images for filter-based -webkit-box-reflect.

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 2000 matching lines @@
             'paint/BlockPainter.cpp',
             'paint/BlockPainter.h',
             'paint/BoxBorderPainter.cpp',
             'paint/BoxBorderPainter.h',
             'paint/BoxClipper.cpp',
             'paint/BoxClipper.h',
             'paint/BoxDecorationData.cpp',
             'paint/BoxDecorationData.h',
             'paint/BoxPainter.cpp',
             'paint/BoxPainter.h',
+            'paint/BoxReflectionUtils.cpp',
+            'paint/BoxReflectionUtils.h',
             'paint/ClipScope.cpp',
             'paint/ClipScope.h',
             'paint/DetailsMarkerPainter.cpp',
             'paint/DetailsMarkerPainter.h',
             'paint/EllipsisBoxPainter.cpp',
             'paint/EllipsisBoxPainter.h',
             'paint/EmbeddedObjectPainter.cpp',
             'paint/EmbeddedObjectPainter.h',
             'paint/FieldsetPainter.cpp',
             'paint/FieldsetPainter.h',
@@ skipping 2063 matching lines @@
             'svg/SVGPathParserTest.cpp',
             'svg/UnsafeSVGAttributeSanitizationTest.cpp',
             'testing/PrivateScriptTestTest.cpp',
             'timing/MemoryInfoTest.cpp',
             'workers/WorkerThreadTest.cpp',
             'workers/WorkerThreadTestHelper.h',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }