Fix assert failure in AnimatableStrokeDasharrayList::equalTo()

Source/core/animation/AnimatableRepeatable.h

Index: Source/core/animation/AnimatableRepeatable.h
diff --git a/Source/core/animation/AnimatableRepeatable.h b/Source/core/animation/AnimatableRepeatable.h
index c0418073d2dc5cb9d848563e5c8217478124d83d..6d1747116666aac96d03d536a293179739755e93 100644
--- a/Source/core/animation/AnimatableRepeatable.h
+++ b/Source/core/animation/AnimatableRepeatable.h
@@ -74,7 +74,8 @@ private:
 
 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);
 }