Made CSSPropertyAPIWillChange which implements API for will-change

third_party/WebKit/Source/core/css/properties/CSSPropertyAPIWillChange.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/CSSPropertyAPIWillChange.h"
+
+#include "core/css/CSSValueList.h"
+#include "core/css/parser/CSSParserTokenRange.h"
+#include "core/css/parser/CSSPropertyParser.h"
+#include "core/css/parser/CSSPropertyParserHelpers.h"
+
+namespace blink {
+
+const CSSValue* CSSPropertyAPIWillChange::parseSingleValue(
+    CSSParserTokenRange& range,
+    const CSSParserContext& context) {
+  if (range.peek().id() == CSSValueAuto)
+    return CSSPropertyParserHelpers::consumeIdent(range);
+
+  CSSValueList* values = CSSValueList::createCommaSeparated();
+  // Every comma-separated list of identifiers is a valid will-change value,
+  // unless the list includes an explicitly disallowed identifier.
+  while (true) {
+    if (range.peek().type() != IdentToken)
+      return nullptr;
+    CSSPropertyID unresolvedProperty =
+        unresolvedCSSPropertyID(range.peek().value());
+    if (unresolvedProperty != CSSPropertyInvalid &&
+        unresolvedProperty != CSSPropertyVariable) {
+      DCHECK(CSSPropertyMetadata::isEnabledProperty(unresolvedProperty));
+      // Now "all" is used by both CSSValue and CSSPropertyValue.
+      // Need to return nullptr when currentValue is CSSPropertyAll.
+      if (unresolvedProperty == CSSPropertyWillChange ||
+          unresolvedProperty == CSSPropertyAll)
+        return nullptr;
+      values->append(*CSSCustomIdentValue::create(unresolvedProperty));
+      range.consumeIncludingWhitespace();
+    } else {
+      switch (range.peek().id()) {
+        case CSSValueNone:
+        case CSSValueAll:
+        case CSSValueAuto:
+        case CSSValueDefault:
+        case CSSValueInitial:
+        case CSSValueInherit:
+          return nullptr;
+        case CSSValueContents:
+        case CSSValueScrollPosition:
+          values->append(*CSSPropertyParserHelpers::consumeIdent(range));
+          break;
+        default:
+          range.consumeIncludingWhitespace();
+          break;
+      }
+    }
+
+    if (range.atEnd())
+      break;
+    if (!CSSPropertyParserHelpers::consumeCommaIncludingWhitespace(range))
+      return nullptr;
+  }
+
+  return values;
+}
+
+}  // namespace blink