Proof of concept that CSSPropertyAPI*::parseSingleValue may need more tahn 2 arguments

third_party/WebKit/Source/core/css/properties/CSSPropertyAPIBackgroundComponent.cpp

+// 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.
+
+#include "core/css/properties/CSSPropertyAPIBackgroundComponent.h"
+
+#include "core/css/parser/CSSPropertyParserHelpers.h"
+#include "core/css/properties/CSSPropertyBackgroundComponentUtils.h"
+
+namespace blink {
+
+const CSSValue* CSSPropertyAPIBackgroundComponent::parseSingleValue(
+    CSSPropertyID unresolvedProperty,
+    CSSParserTokenRange& range,
+    const CSSParserContext* context) {
+  CSSValue* result = nullptr;
+  do {
+    CSSValue* value =
+        CSSPropertyBackgroundComponentUtils::consumeBackgroundComponent(
+            unresolvedProperty, range, context);
+    if (!value)
+      return nullptr;
+    CSSPropertyBackgroundComponentUtils::addBackgroundValue(result, value);
+  } while (CSSPropertyParserHelpers::consumeCommaIncludingWhitespace(range));
+  return result;
+}
+
+}  // namespace blink