Make scrollAnimatorEnabled work on Mac like it does on other platforms

third_party/WebKit/public/web/mac/WebScrollbarTheme.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 36 matching lines @@
     // Updates the scrollbar appearance and behavior.
     // |initialButtonDelay| is the current value of NSScrollerButtonDelay from NSUserDefaults.
     // |autoscrollButtonDelay| is the current value of NSScrollerButtonPeriod from NSUserDefaults.
     // |preferredScrollerStyle| is the current value of +[NSScroller preferredScrollerStyle].
     // |redraw| is true if the update requires a redraw to include the change.
     // |scrollAnimationEnabled| is the current value of NSScrollAnimationEnabled or AppleScrollAnimationEnabled from NSUserDefaults.
     // |buttonPlacement| is the current value of AppleScrollBarVariant
     BLINK_EXPORT static void updateScrollbarsWithNSDefaults(
         float initialButtonDelay, float autoscrollButtonDelay,
         ScrollerStyle preferredScrollerStyle, bool redraw,
-        bool scrollAnimationEnabled, WebScrollbarButtonsPlacement);
+        WebScrollbarButtonsPlacement);
 };
 
 } // namespace blink
 
 #endif