Added CSSPropertyCounterUtils which holds shared counter parsing logic.

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

Index: third_party/WebKit/Source/core/css/properties/CSSPropertyCounterUtils.cpp
diff --git a/third_party/WebKit/Source/core/css/properties/CSSPropertyCounterUtils.cpp b/third_party/WebKit/Source/core/css/properties/CSSPropertyCounterUtils.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..e8191c569296e04d2166aa0c0a843ea55e8da64e
--- /dev/null
+++ b/third_party/WebKit/Source/core/css/properties/CSSPropertyCounterUtils.cpp
@@ -0,0 +1,38 @@
+// Copyright 2017 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/CSSPropertyCounterUtils.h"
+
+#include "core/css/CSSValueList.h"
+#include "core/css/CSSValuePair.h"
+#include "core/css/parser/CSSParserTokenRange.h"
+#include "core/css/parser/CSSPropertyParserHelpers.h"
+
+namespace blink {
+
+CSSValue* CSSPropertyCounterUtils::consumeCounter(
+    CSSParserTokenRange& range,
+    CounterDefaultValue defaultValue) {
+  if (range.peek().id() == CSSValueNone)
+    return CSSPropertyParserHelpers::consumeIdent(range);
+
+  CSSValueList* list = CSSValueList::createSpaceSeparated();
+  do {
+    CSSCustomIdentValue* counterName =
+        CSSPropertyParserHelpers::consumeCustomIdent(range);
+    if (!counterName)
+      return nullptr;
+    int i = static_cast<int>(defaultValue);

[shend, 2017/03/28 01:58:48]

Could we change 'i' to a more informative name e.g. value?

+    if (CSSPrimitiveValue* counterValue =
+            CSSPropertyParserHelpers::consumeInteger(range))
+      i = clampTo<int>(counterValue->getDoubleValue());
+    list->append(*CSSValuePair::create(
+        counterName,
+        CSSPrimitiveValue::create(i, CSSPrimitiveValue::UnitType::Integer),
+        CSSValuePair::DropIdenticalValues));
+  } while (!range.atEnd());
+  return list;
+}
+
+}  // namespace blink