Change first() and second() in CSSPairValue to return const references

Source/core/css/CSSValuePair.h

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006 Apple Computer, Inc.
  *
  * 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 29 matching lines @@
         IdenticalValuesPolicy identicalValuesPolicy)
     {
         return adoptRefWillBeNoop(new CSSValuePair(first, second, identicalValuesPolicy));
     }
 
     static PassRefPtrWillBeRawPtr<CSSValuePair> create(const LengthSize& lengthSize, const ComputedStyle& style)
     {
         return adoptRefWillBeNoop(new CSSValuePair(CSSPrimitiveValue::create(lengthSize.width(), style.effectiveZoom()), CSSPrimitiveValue::create(lengthSize.height(), style.effectiveZoom()), KeepIdenticalValues));
     }
 
-    CSSValue* first() const { return m_first.get(); }
-    CSSValue* second() const { return m_second.get(); }
+    // TODO(sashab): Remove these non-const versions.
+    CSSValue& first() { return *m_first; }
+    CSSValue& second() { return *m_second; }
+    const CSSValue& first() const { return *m_first; }
+    const CSSValue& second() const { return *m_second; }
 
     String customCSSText() const
     {
         String first = m_first->cssText();
         String second = m_second->cssText();
         if (m_identicalValuesPolicy == DropIdenticalValues && first == second)
             return first;
         return first + ' ' + second;
     }
 
     bool equals(const CSSValuePair& other) const
     {
         ASSERT(m_identicalValuesPolicy == other.m_identicalValuesPolicy);
         return compareCSSValuePtr(m_first, other.m_first)
             && compareCSSValuePtr(m_second, other.m_second);
     }
 
     DECLARE_TRACE_AFTER_DISPATCH();
 
 private:
     CSSValuePair(PassRefPtrWillBeRawPtr<CSSValue> first, PassRefPtrWillBeRawPtr<CSSValue> second, IdenticalValuesPolicy identicalValuesPolicy)
         : CSSValue(ValuePairClass)
         , m_first(first)
         , m_second(second)
-        , m_identicalValuesPolicy(identicalValuesPolicy) { }
+        , m_identicalValuesPolicy(identicalValuesPolicy)
+    {
+        ASSERT(m_first);
+        ASSERT(m_second);
+    }
 
     RefPtrWillBeMember<CSSValue> m_first;
     RefPtrWillBeMember<CSSValue> m_second;
     IdenticalValuesPolicy m_identicalValuesPolicy;
 };
 
 DEFINE_CSS_VALUE_TYPE_CASTS(CSSValuePair, isValuePair());
 
 } // namespace
 
 #endif // CSSValuePair_h