Simplify animation/transition parsing slightly

Source/core/css/parser/BisonCSSParser-in.cpp

 /*
  * Copyright (C) 2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Nicholas Shanks <webkit@nickshanks.com>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2012 Adobe Systems Incorporated. All rights reserved.
  * Copyright (C) 2012 Intel Corporation. All rights reserved.
  *
@@ skipping 903 matching lines @@
 }
 
 PassRefPtrWillBeRawPtr<CSSValue> BisonCSSParser::parseAnimationTimingFunctionValue(const String& string)
 {
     if (string.isEmpty())
         return nullptr;
     RefPtrWillBeRawPtr<MutableStylePropertySet> style = MutableStylePropertySet::create();
     if (!parseValue(style.get(), CSSPropertyTransitionTimingFunction, string, false, HTMLStandardMode, 0))
         return nullptr;
 
-    return style->getPropertyCSSValue(CSSPropertyTransitionTimingFunction);
+    RefPtrWillBeRawPtr<CSSValue> value = style->getPropertyCSSValue(CSSPropertyTransitionTimingFunction);
+    if (!value || value->isInitialValue() || value->isInheritedValue())
+        return nullptr;
+    CSSValueList* valueList = toCSSValueList(value.get());
+    if (valueList->length() > 1)
+        return nullptr;
+    return valueList->item(0);
 }
 
 bool BisonCSSParser::parseValue(MutableStylePropertySet* declaration, CSSPropertyID propertyID, const String& string, bool important, const Document& document)
 {
     ASSERT(!string.isEmpty());
 
     CSSParserContext context(document, UseCounter::getFrom(&document));
 
     if (parseSimpleLengthValue(declaration, propertyID, string, important, context.mode()))
         return true;
@@ skipping 1134 matching lines @@
     rule->setProperties(createStylePropertySet());
     clearProperties();
 
     StyleRuleViewport* result = rule.get();
     m_parsedRules.append(rule.release());
 
     return result;
 }
 
 }