Added CSSPropertyCounterUtils which holds shared counter parsing logic.

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

+// 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 value = static_cast<int>(defaultValue);

[suzyh_UTC10 (ex-contributor), 2017/03/28 02:26:08]

This int-iness enum-iness arrangement is a bit weird. It's not clear to me that
the concept of an enum is what you're looking for here, even though the values
are consecutive integers. I think two named integer constants would be a better
approach, and would avoid the static_cast.

+    if (CSSPrimitiveValue* counterValue =
+            CSSPropertyParserHelpers::consumeInteger(range))
+      value = clampTo<int>(counterValue->getDoubleValue());

[suzyh_UTC10 (ex-contributor), 2017/03/28 02:26:08]

Would it make sense to use getIntValue() instead then?

[Bugs Nash, 2017/03/28 02:32:50]

I think we're experiencing creep here? This is a refactor that moves code from
one place to another, and I don't believe the intention of Ribbon is to fix all
the problems in all the methods at the same time. What do you think?

+    list->append(*CSSValuePair::create(
+        counterName,
+        CSSPrimitiveValue::create(value, CSSPrimitiveValue::UnitType::Integer),
+        CSSValuePair::DropIdenticalValues));
+  } while (!range.atEnd());
+  return list;
+}
+
+}  // namespace blink