First past at removing writing mode.

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 77 matching lines @@
 font-size animatable, inherited, custom_all
 font-stretch inherited, font, type_name=FontStretch, name_for_methods=Stretch
 font-style inherited, font, type_name=FontStyle, name_for_methods=Style
 font-variant inherited, font, type_name=FontVariant, name_for_methods=Variant
 font-variant-ligatures inherited, font, name_for_methods=VariantLigatures, converter=convertFontVariantLigatures
 font-weight animatable, inherited, font, type_name=FontWeight, name_for_methods=Weight, converter=convertFontWeight
 -webkit-font-feature-settings inherited, font, name_for_methods=FeatureSettings, converter=convertFontFeatureSettings
 -webkit-font-smoothing inherited, font, type_name=FontSmoothingMode
 -webkit-locale inherited, custom_value
 -webkit-text-orientation inherited, custom_value
--webkit-writing-mode inherited, custom_value
 text-rendering inherited, font, type_name=TextRenderingMode
 zoom animatable, custom_all
 line-height animatable, inherited, getter=specifiedLineHeight, custom_value
 
 align-content
 align-items custom_all
 align-self custom_all
 backface-visibility
 background-attachment custom_all
 background-blend-mode custom_all
@@ skipping 316 matching lines @@
 
 // Aliases; these map to the same CSSPropertyID
 
 -epub-caption-side alias_for=caption-side
 -epub-text-combine alias_for=-webkit-text-combine
 -epub-text-emphasis alias_for=-webkit-text-emphasis
 -epub-text-emphasis-color alias_for=-webkit-text-emphasis-color
 -epub-text-emphasis-style alias_for=-webkit-text-emphasis-style
 -epub-text-orientation alias_for=-webkit-text-orientation
 -epub-word-break alias_for=word-break
--epub-writing-mode alias_for=-webkit-writing-mode
 -webkit-align-content alias_for=align-content
 -webkit-align-items alias_for=align-items
 -webkit-align-self alias_for=align-self
 -webkit-border-bottom-left-radius alias_for=border-bottom-left-radius
 -webkit-border-bottom-right-radius alias_for=border-bottom-right-radius
 -webkit-border-top-left-radius alias_for=border-top-left-radius
 -webkit-border-top-right-radius alias_for=border-top-right-radius
 -webkit-box-sizing alias_for=box-sizing
 -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
 -webkit-shape-image-threshold alias_for=shape-image-threshold
 -webkit-shape-margin alias_for=shape-margin
 -webkit-shape-outside alias_for=shape-outside