Implements CSSPropertyAPI for the text-underline-position property.

third_party/WebKit/Source/core/css/CSSProperties.in

Index: third_party/WebKit/Source/core/css/CSSProperties.in
diff --git a/third_party/WebKit/Source/core/css/CSSProperties.in b/third_party/WebKit/Source/core/css/CSSProperties.in
index 5a30f1d12c91ff5829f49551efb436e9ff33374d..423e8135de91cf6ca0b2dc3e85244253c43fe9c2 100644
--- a/third_party/WebKit/Source/core/css/CSSProperties.in
+++ b/third_party/WebKit/Source/core/css/CSSProperties.in
@@ -373,7 +373,7 @@ text-overflow type_name=TextOverflow
 text-shadow interpolable, inherited, converter=convertShadow
 text-size-adjust inherited, converter=convertTextSizeAdjust, type_name=TextSizeAdjust
 text-transform inherited, keyword_only, keywords=[capitalize|uppercase|lowercase|none], initial_keyword=none
-text-underline-position runtime_flag=CSS3TextDecorations, inherited, type_name=TextUnderlinePosition
+text-underline-position runtime_flag=CSS3TextDecorations, inherited, type_name=TextUnderlinePosition, api_class
 top typedom_types=[Length], keywords=[auto], supports_percentage, interpolable, initial=initialOffset, converter=convertLengthOrAuto
 touch-action converter=convertFlags<TouchAction>, type_name=TouchAction
 transform typedom_types=[Transform], keywords=[none], interpolable, converter=convertTransformOperations