Remove WebAnimationsElementAnimate runtime flag (status=stable)

Source/core/animation/ElementAnimation.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 91 matching lines @@
             ASSERT(it->key->source());
             if (it->key->source()->isCurrent())
                 animationPlayers.append(it->key);
         }
         return animationPlayers;
     }
 
 private:
     static AnimationPlayer* animateInternal(Element& element, PassRefPtrWillBeRawPtr<AnimationEffect> effect, const Timing& timing)
     {
-        if (RuntimeEnabledFeatures::webAnimationsElementAnimateEnabled()) {
-            RefPtrWillBeRawPtr<Animation> animation = Animation::create(&element, effect, timing);
-            return element.document().timeline().play(animation.get());
-        }
-        return 0;
+        RefPtrWillBeRawPtr<Animation> animation = Animation::create(&element, effect, timing);
+        return element.document().timeline().play(animation.get());
     }
 };
 
 } // namespace blink
 
 #endif // ElementAnimation_h