Unprefix -webkit-filter and add a pixel test for it.

sky/engine/core/css/CSSProperties.in

 // This file specifies all the CSS properties we support and the necessary
 // information for our code generation. The various supported arguments
 // are described below with example usage
 
 
 // - alias_for=other-property
 // Properties specifying alias_for do not get their own enum and instead map
 // directly onto the CSSPropertyID they alias. Currently this means that the
 // UseCounter will not pick up on these (crbug.com/304855)
 
@@ skipping 203 matching lines @@
 unicode-bidi
 vertical-align animatable, custom_inherit, custom_value
 animation-delay custom_all
 animation-direction custom_all
 animation-duration custom_all
 animation-fill-mode custom_all
 animation-iteration-count custom_all
 animation-name custom_all
 animation-play-state custom_all
 animation-timing-function custom_all
+filter animatable, custom_value
 -webkit-aspect-ratio inherited, custom_all
 -webkit-backface-visibility use_handlers_for=CSSPropertyBackfaceVisibility
 -webkit-background-clip use_handlers_for=CSSPropertyBackgroundClip
 -webkit-background-composite custom_all
 -webkit-background-origin use_handlers_for=CSSPropertyBackgroundOrigin
 -webkit-background-size animatable, use_handlers_for=CSSPropertyBackgroundSize
 -webkit-border-horizontal-spacing animatable, inherited, name_for_methods=HorizontalBorderSpacing, converter=convertComputedLength<short>
 -webkit-border-image initial=initialNinePieceImage, custom_value
 -webkit-border-vertical-spacing animatable, inherited, name_for_methods=VerticalBorderSpacing, converter=convertComputedLength<short>
 -webkit-box-decoration-break
 -webkit-box-shadow animatable, use_handlers_for=CSSPropertyBoxShadow
 -webkit-clip-path animatable, custom_value
--webkit-filter animatable, custom_value
 -webkit-highlight inherited, converter=convertString<CSSValueNone>
 -webkit-hyphenate-character inherited, name_for_methods=HyphenationString, converter=convertString<CSSValueAuto>
 -webkit-line-box-contain inherited, converter=convertLineBoxContain
 -webkit-line-break inherited, type_name=LineBreak
 -webkit-mask-box-image-outset animatable, custom_all
 -webkit-mask-box-image-repeat custom_all
 -webkit-mask-box-image-slice animatable, custom_all
 -webkit-mask-box-image-source animatable, custom_value
 -webkit-mask-box-image-width animatable, custom_all
 -webkit-mask-clip custom_all
@@ skipping 137 matching lines @@
 -webkit-flex alias_for=flex
 -webkit-flex-basis alias_for=flex-basis
 -webkit-flex-direction alias_for=flex-direction
 -webkit-flex-flow alias_for=flex-flow
 -webkit-flex-grow alias_for=flex-grow
 -webkit-flex-shrink alias_for=flex-shrink
 -webkit-flex-wrap alias_for=flex-wrap
 -webkit-justify-content alias_for=justify-content
 -webkit-opacity alias_for=opacity
 -webkit-order alias_for=order