Include AvailabilityMacros.h only where it is used.

Source/core/platform/mac/NSScrollerImpDetails.h

 /*
  * Copyright (C) 2011 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
  */
 
 #ifndef WebCore_NSScrollerImpDetails_h
 #define WebCore_NSScrollerImpDetails_h
 
 #include "config.h"
+#import <AvailabilityMacros.h>
 
 // Public APIs not available on versions of Mac on which we build
 #if __MAC_OS_X_VERSION_MAX_ALLOWED == 1060
 enum {
     NSScrollerStyleLegacy       = 0,
     NSScrollerStyleOverlay      = 1
 };
 typedef NSInteger NSScrollerStyle;
 
 enum {
@@ skipping 70 matching lines @@
 
 namespace WebCore {
 
 bool isScrollbarOverlayAPIAvailable();
 
 NSScrollerStyle recommendedScrollerStyle();
 
 }
 
 #endif