Remove CSSOM mutability in StyleRule.

sky/engine/core/css/StyleKeyframe.cpp

 /*
  * Copyright (C) 2007, 2008, 2012 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 71 matching lines @@
 }
 
 void StyleKeyframe::setKeys(PassOwnPtr<Vector<double> > keys)
 {
     ASSERT(keys && !keys->isEmpty());
     m_keys = keys;
     m_keyText = String();
     ASSERT(m_keyText.isNull());
 }
 
-MutableStylePropertySet& StyleKeyframe::mutableProperties()
-{
-    if (!m_properties->isMutable())
-        m_properties = m_properties->mutableCopy();
-    return *toMutableStylePropertySet(m_properties.get());
-}
-
 void StyleKeyframe::setProperties(PassRefPtr<StylePropertySet> properties)
 {
     ASSERT(properties);
     m_properties = properties;
 }
 
 String StyleKeyframe::cssText() const
 {
     StringBuilder result;
     result.append(keyText());
@@ skipping 18 matching lines @@
             // or values higher than 100%, then the keyframe will be ignored."
             keyVector->clear();
             break;
         }
         keyVector->at(i) = key / 100;
     }
     return keyVector.release();
 }
 
 } // namespace blink