Move preferred scrollbar style preference change listening from renderer to browser, 3 of 3.

Source/platform/mac/NSScrollerImpDetails.mm

-/*
- * Copyright (C) 2011 Apple Inc. All Rights Reserved.
- * Copyright (C) 2011 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:
- * 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.
- */
-
-
-#include "config.h"
-#include "RuntimeEnabledFeatures.h"
-#include "platform/mac/NSScrollerImpDetails.h"
-
-namespace {
-
-// Declare notification names from the 10.7 SDK.
-#if !defined(MAC_OS_X_VERSION_10_7) || MAC_OS_X_VERSION_MAX_ALLOWED < MAC_OS_X_VERSION_10_7
-NSString* NSPreferredScrollerStyleDidChangeNotification = @"NSPreferredScrollerStyleDidChangeNotification";
-#endif
-
-// Storing the current NSScrollerStyle as a global is appreciably faster than
-// having it be a property of ScrollerStylerObserver.
-NSScrollerStyle g_scrollerStyle = NSScrollerStyleLegacy;
-
-}  // anonymous namespace
-
-@interface ScrollerStyleObserver : NSObject
-- (id)init;
-- (void)preferredScrollerStyleDidChange:(NSNotification*)notification;
-@end
-
-@implementation ScrollerStyleObserver
-- (id)init
-{
-    if ((self = [super init])) {
-        if ([NSScroller respondsToSelector:@selector(preferredScrollerStyle)]) {
-            g_scrollerStyle = [NSScroller preferredScrollerStyle];
-            NSNotificationCenter* center = [NSNotificationCenter defaultCenter];
-            [center addObserver:self
-                       selector:@selector(preferredScrollerStyleDidChange:)
-                           name:NSPreferredScrollerStyleDidChangeNotification
-                         object:nil];
-        }
-    }
-    return self;
-}
-
-- (void)preferredScrollerStyleDidChange:(NSNotification*)notification
-{
-    g_scrollerStyle = [NSScroller preferredScrollerStyle];
-}
-@end
-
-namespace WebCore {
-
-bool isScrollbarOverlayAPIAvailable()
-{
-    static bool apiAvailable =
-        [NSClassFromString(@"NSScrollerImp") respondsToSelector:@selector(scrollerImpWithStyle:controlSize:horizontal:replacingScrollerImp:)]
-        && [NSClassFromString(@"NSScrollerImpPair") instancesRespondToSelector:@selector(scrollerStyle)];
-    return apiAvailable;
-}
-
-NSScrollerStyle recommendedScrollerStyle()
-{
-    if (RuntimeEnabledFeatures::overlayScrollbarsEnabled())
-        return NSScrollerStyleOverlay;
-
-    // The ScrollerStyleObserver will update g_scrollerStyle at init and when needed.
-    // This function is hot.
-    // http://crbug.com/303205
-    static ScrollerStyleObserver* scrollerStyleObserver = [[ScrollerStyleObserver alloc] init];
-    (void)scrollerStyleObserver;
-    return g_scrollerStyle;
-}
-
-}