Add position: sticky as supported position value when CSSStickyPosition is enabled.

Source/core/css/parser/CSSParserFastPaths.cpp

 // Copyright 2014 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 "config.h"
 #include "core/css/parser/CSSParserFastPaths.h"
 
 #include "core/StylePropertyShorthand.h"
 #include "core/css/CSSFunctionValue.h"
 #include "core/css/CSSValuePool.h"
@@ skipping 518 matching lines @@
     case CSSPropertyWebkitColumnBreakAfter:
     case CSSPropertyWebkitColumnBreakBefore:
         return valueID == CSSValueAuto || valueID == CSSValueAlways || valueID == CSSValueAvoid || valueID == CSSValueLeft || valueID == CSSValueRight;
     case CSSPropertyPageBreakInside: // avoid | auto
     case CSSPropertyWebkitColumnBreakInside:
         return valueID == CSSValueAuto || valueID == CSSValueAvoid;
     case CSSPropertyPointerEvents:
         // none | visiblePainted | visibleFill | visibleStroke | visible |
         // painted | fill | stroke | auto | all | bounding-box
         return valueID == CSSValueVisible || valueID == CSSValueNone || valueID == CSSValueAll || valueID == CSSValueAuto || (valueID >= CSSValueVisiblePainted && valueID <= CSSValueBoundingBox);
-    case CSSPropertyPosition: // static | relative | absolute | fixed
-        return valueID == CSSValueStatic || valueID == CSSValueRelative || valueID == CSSValueAbsolute || valueID == CSSValueFixed;
+    case CSSPropertyPosition: // static | relative | absolute | fixed | sticky
+        return valueID == CSSValueStatic || valueID == CSSValueRelative || valueID == CSSValueAbsolute || valueID == CSSValueFixed || (RuntimeEnabledFeatures::cssStickyPositionEnabled() && valueID == CSSValueSticky);
     case CSSPropertyResize: // none | both | horizontal | vertical | auto
         return valueID == CSSValueNone || valueID == CSSValueBoth || valueID == CSSValueHorizontal || valueID == CSSValueVertical || valueID == CSSValueAuto;
     case CSSPropertyScrollBehavior: // auto | smooth
         ASSERT(RuntimeEnabledFeatures::cssomSmoothScrollEnabled());
         return valueID == CSSValueAuto || valueID == CSSValueSmooth;
     case CSSPropertySpeak: // none | normal | spell-out | digits | literal-punctuation | no-punctuation
         return valueID == CSSValueNone || valueID == CSSValueNormal || valueID == CSSValueSpellOut || valueID == CSSValueDigits || valueID == CSSValueLiteralPunctuation || valueID == CSSValueNoPunctuation;
     case CSSPropertyTableLayout: // auto | fixed
         return valueID == CSSValueAuto || valueID == CSSValueFixed;
     case CSSPropertyTextAlignLast:
@@ skipping 398 matching lines @@
     if (isColorPropertyID(propertyID))
         return parseColor(string, isQuirksModeBehavior(parserMode));
     if (RefPtrWillBeRawPtr<CSSValue> keyword = parseKeywordValue(propertyID, string))
         return keyword.release();
     if (RefPtrWillBeRawPtr<CSSValue> transform = parseSimpleTransform(propertyID, string))
         return transform.release();
     return nullptr;
 }
 
 } // namespace blink