Refactored out need to pass property ID in background list parsing.

third_party/WebKit/Source/core/css/parser/CSSPropertyParserHelpers.cpp

Index: third_party/WebKit/Source/core/css/parser/CSSPropertyParserHelpers.cpp
diff --git a/third_party/WebKit/Source/core/css/parser/CSSPropertyParserHelpers.cpp b/third_party/WebKit/Source/core/css/parser/CSSPropertyParserHelpers.cpp
index 9a507a3893c44883644fdc262fdded61f0a5c292..b9806e31d9cc41df5b8d75979399a6e6c87c72ce 100644
--- a/third_party/WebKit/Source/core/css/parser/CSSPropertyParserHelpers.cpp
+++ b/third_party/WebKit/Source/core/css/parser/CSSPropertyParserHelpers.cpp
@@ -1458,6 +1458,20 @@ CSSIdentifierValue* ConsumeShapeBox(CSSParserTokenRange& range) {
                       CSSValueMarginBox>(range);
 }
 
+void AddListValueOptimized(CSSValue*& list, CSSValue* value) {

[suzyh_UTC10 (ex-contributor), 2017/06/05 00:49:20]

No action required, since this is not new to your patch. Just felt a need to say
'ew'. I didn't realise you could have a reference to a pointer >.<

[Bugs Nash, 2017/06/05 01:20:50]

this is required because we need to change what the pointer points to (see line
1465) and this needs to be reflected in the call site

+  if (list) {
+    if (!list->IsBaseValueList()) {
+      CSSValue* first_value = list;
+      list = CSSValueList::CreateCommaSeparated();
+      ToCSSValueList(list)->Append(*first_value);
+    }
+    ToCSSValueList(list)->Append(*value);
+  } else {
+    // To conserve memory we don't actually wrap a single value in a list.
+    list = value;
+  }
+}
+
 }  // namespace CSSPropertyParserHelpers
 
 }  // namespace blink