Made CSSPrimitiveValue::getString() only work for String types

Source/core/css/CSSPrimitiveValue.cpp

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2012 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 784 matching lines @@
 }
 
 String CSSPrimitiveValue::getStringValue() const
 {
     switch (type()) {
     case UnitType::CustomIdentifier:
     case UnitType::String:
     case UnitType::Attribute:
     case UnitType::URI:
         return m_value.string;
-    case UnitType::ValueID:
-        return valueName(m_value.valueID);
-    case UnitType::PropertyID:
-        return propertyName(m_value.propertyID);
     default:
         break;
     }
 
+    ASSERT_NOT_REACHED();
     return String();
 }
 
 static String formatNumber(double number, const char* suffix, unsigned suffixLength)
 {
 #if OS(WIN) && _MSC_VER < 1900
     unsigned oldFormat = _set_output_format(_TWO_DIGIT_EXPONENT);
 #endif
     String result = String::format("%.6g", number);
 #if OS(WIN) && _MSC_VER < 1900
@@ skipping 286 matching lines @@
         visitor->trace(m_value.shape);
         break;
     default:
         break;
     }
 #endif
     CSSValue::traceAfterDispatch(visitor);
 }
 
 } // namespace blink