MacViews: Overlay Scrollbars with Show/Hide Animations

ui/base/test/scoped_preferred_scroller_style_legacy_mac.mm

-// Copyright 2016 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.
-
-#import "ui/base/test/scoped_preferred_scroller_style_legacy_mac.h"
-
-#import "base/mac/sdk_forward_declarations.h"
-#import "base/mac/scoped_objc_class_swizzler.h"
-
-using base::mac::ScopedObjCClassSwizzler;
-
-namespace {
-
-void NotifyStyleChanged() {
-  [[NSNotificationCenter defaultCenter]
-      postNotificationName:NSPreferredScrollerStyleDidChangeNotification
-                    object:nil];
-}
-
-}  // namespace
-
-// Donates a testing implementation of +[NSScroller preferredScrollerStyle].
-@interface FakeNSScrollerPreferredStyleDonor : NSObject
-@end
-
-@implementation FakeNSScrollerPreferredStyleDonor
-
-+ (NSInteger)preferredScrollerStyle {
-  return NSScrollerStyleLegacy;
-}
-
-@end
-
-namespace ui {
-namespace test {
-
-ScopedPreferredScrollerStyleLegacy::ScopedPreferredScrollerStyleLegacy() {
-  if (![NSScroller respondsToSelector:@selector(preferredScrollerStyle)])
-    return;
-
-  NSInteger previous_style = [NSScroller preferredScrollerStyle];
-
-  swizzler_.reset(
-      new ScopedObjCClassSwizzler([NSScroller class],
-                                  [FakeNSScrollerPreferredStyleDonor class],
-                                  @selector(preferredScrollerStyle)));
-
-  if (previous_style != NSScrollerStyleLegacy)
-    NotifyStyleChanged();
-}
-
-ScopedPreferredScrollerStyleLegacy::~ScopedPreferredScrollerStyleLegacy() {
-  if (!swizzler_)
-    return;  // Handle 10.6, which wouldn't have swizzled anything.
-
-  swizzler_.reset();
-
-  if ([NSScroller preferredScrollerStyle] != NSScrollerStyleLegacy)
-    NotifyStyleChanged();
-}
-
-}  // namespace test
-}  // namespace ui