WIP Add memory optimisation option to ConsumeCommaSeparatedList

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CSSPropertyParserHelpers_h
 #define CSSPropertyParserHelpers_h
 
 #include "core/css/CSSCustomIdentValue.h"
 #include "core/css/CSSIdentifierValue.h"
 #include "core/css/CSSPrimitiveValue.h"
@@ skipping 108 matching lines @@
   if (range.Peek().GetType() != kIdentToken ||
       !IdentMatches<names...>(range.Peek().Id()))
     return nullptr;
   return CSSIdentifierValue::Create(range.ConsumeIncludingWhitespace().Id());
 }
 
 // ConsumeCommaSeparatedList takes a callback function to call on each item in
 // the list, followed by the arguments to pass to this callback.
 // The first argument to the callback must be the CSSParserTokenRange
 template <typename Func, typename... Args>
-CSSValueList* ConsumeCommaSeparatedList(Func callback,
-                                        CSSParserTokenRange& range,
-                                        Args... args) {
-  CSSValueList* list = CSSValueList::CreateCommaSeparated();
+CSSValue* ConsumeCommaSeparatedList(bool optimise,
+                                    Func callback,
+                                    CSSParserTokenRange& range,
+                                    Args... args) {
+  CSSValue* result = nullptr;
+  if (!optimise)
+    result = CSSValueList::CreateCommaSeparated();
   do {
     CSSValue* value = callback(range, args...);
     if (!value)
       return nullptr;
-    list->Append(*value);
+
+    if (optimise) {
+      if (!result) {
+        // To conserve memory we don't wrap a single value in a list.
+        result = value;
+        continue;
+      }
+      if (!result->IsBaseValueList()) {
+        CSSValue* first_value = result;
+        result = CSSValueList::CreateCommaSeparated();
+        ToCSSValueList(result)->Append(*first_value);
+      }
+    }
+    ToCSSValueList(result)->Append(*value);
   } while (ConsumeCommaIncludingWhitespace(range));
-  DCHECK(list->length());
-  return list;
+
+  DCHECK(!result->IsBaseValueList() || ToCSSValueList(result)->length());
+  return result;
 }
 
 }  // namespace CSSPropertyParserHelpers
 
 }  // namespace blink
 
 #endif  // CSSPropertyParserHelpers_h