Make scrollAnimatorEnabled work on Mac like it does on other platforms

base/mac/mac_util.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_MAC_MAC_UTIL_H_
 #define BASE_MAC_MAC_UTIL_H_
 
 #include <AvailabilityMacros.h>
 #include <Carbon/Carbon.h>
 #include <stdint.h>
@@ skipping 226 matching lines @@
 // failure.
 BASE_EXPORT std::string GetModelIdentifier();
 
 // Parse a model identifier string; for example, into ("MacBookPro", 6, 1).
 // If any error occurs, none of the input pointers are touched.
 BASE_EXPORT bool ParseModelIdentifier(const std::string& ident,
                                       std::string* type,
                                       int32_t* major,
                                       int32_t* minor);
 
+// Get the system setting determining whether scroll animations (e.g. when
+// user uses home/end keys) should be enabled.
+BASE_EXPORT bool IsScrollAnimationEnabled();
+
 }  // namespace mac
 }  // namespace base
 
 #endif  // BASE_MAC_MAC_UTIL_H_