Make UseCounters work on aliased properties

Source/core/css/CSSProperties.in

Index: Source/core/css/CSSProperties.in
diff --git a/Source/core/css/CSSProperties.in b/Source/core/css/CSSProperties.in
index 810c1a62c66e43aac8ac7bf620236d9f3280331c..b4c3887cca810b792f844e9f31f218dd8decad40 100644
--- a/Source/core/css/CSSProperties.in
+++ b/Source/core/css/CSSProperties.in
@@ -4,13 +4,14 @@
 
 
 // - 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