Re-land "[css3-text] Implement text-decoration property shorthand"

Source/core/css/CSSParser-in.cpp

Index: Source/core/css/CSSParser-in.cpp
diff --git a/Source/core/css/CSSParser-in.cpp b/Source/core/css/CSSParser-in.cpp
index 048699a5869b59d72a67db754faa483aba12ed32..edbc75075ee64421e897194648fb9f368b0c3791 100644
--- a/Source/core/css/CSSParser-in.cpp
+++ b/Source/core/css/CSSParser-in.cpp
@@ -2114,6 +2114,12 @@ bool CSSParser::parseValue(CSSPropertyID propId, bool important)
     }
 
     case CSSPropertyTextDecoration:
+        // Fall through 'text-decoration-line' parsing if CSS 3 Text Decoration
+        // is disabled to match CSS 2.1 rules for parsing 'text-decoration'.
+        if (RuntimeEnabledFeatures::css3TextDecorationsEnabled()) {
+            // [ <text-decoration-line> || <text-decoration-style> || <text-decoration-color> ] | inherit
+            return parseShorthand(CSSPropertyTextDecoration, textDecorationShorthand(), important);
+        }
     case CSSPropertyWebkitTextDecorationsInEffect:
     case CSSPropertyTextDecorationLine:
         // none | [ underline || overline || line-through || blink ] | inherit
@@ -9029,7 +9035,8 @@ bool CSSParser::parseTextDecoration(CSSPropertyID propId, bool important)
             value = m_valueList->next();
     }
 
-    if (list->length() && isValid) {
+    // Values are either valid or in shorthand scope.
+    if (list->length() && (isValid || inShorthand())) {
         addTextDecorationProperty(propId, list.release(), important);
         return true;
     }