Fix assert failure in AnimatableStrokeDasharrayList::equalTo()

Source/core/animation/AnimatableRepeatable.h

 /*
  * Copyright (C) 2013 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 56 matching lines @@
 private:
     virtual PassRefPtr<AnimatableValue> interpolateTo(const AnimatableValue*, double fraction) const OVERRIDE;
     virtual PassRefPtr<AnimatableValue> addWith(const AnimatableValue*) const OVERRIDE;
 
     virtual AnimatableType type() const OVERRIDE { return TypeRepeatable; }
     virtual bool equalTo(const AnimatableValue*) const OVERRIDE;
 };
 
 inline const AnimatableRepeatable* toAnimatableRepeatable(const AnimatableValue* value)
 {
-    ASSERT_WITH_SECURITY_IMPLICATION(value && value->isRepeatable());
+    // FIXME: Use a better typing system for AnimatableValues that doesn't require ugliness like this to support subclassing.
+    ASSERT_WITH_SECURITY_IMPLICATION(value && (value->isRepeatable() || value->isStrokeDasharrayList()));
     return static_cast<const AnimatableRepeatable*>(value);
 }
 
 } // namespace WebCore
 
 #endif // AnimatableRepeatable_h