Make UseCounters work on aliased properties

Source/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)
+// Properties specifying alias_for should be virtually identical to the
+// properties they alias. Minor parsing differences are allowed as long as
+// the CSSValues created are of the same format of the aliased property.
 
 
 // - runtime_flag=CSSGridLayout
-// The flag on RuntimeEnabledFeatures conditionally enables the property
+// The flag on RuntimeEnabledFeatures conditionally enables the property.
+// This doesn't currently work with alias_for.
 
 
 // - longhands=property;other-property
 // The property is a shorthand for several other properties.
 
 
 // Flags which go into CSSPropertyMetadata:
 // - animatable
 // The animatable flag indicates whether a property can be animated by CSS
 // animations and transitions. If this flag is set, the property should also be
@@ skipping 503 matching lines @@
 -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