MacViews: Overlay Scrollbars with Show/Hide Animations

ui/base/test/scoped_preferred_scroller_style_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_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];
+}
+
+NSScrollerStyle GetScrollerStyle(bool overlay) {
+  return overlay ? NSScrollerStyleOverlay : NSScrollerStyleLegacy;
+}
+
+}  // namespace
+
+// Donates a testing implementation of +[NSScroller preferredScrollerStyle] by
+// returning NSScrollerStyleLegacy.
+@interface FakeNSScrollerPreferredStyleLegacyDonor : NSObject
+@end
+
+@implementation FakeNSScrollerPreferredStyleLegacyDonor
+
++ (NSInteger)preferredScrollerStyle {
+  return NSScrollerStyleLegacy;
+}
+
+@end
+
+// Donates a testing implementation of +[NSScroller preferredScrollerStyle] by
+// returning NSScrollerStyleOverlay.
+@interface FakeNSScrollerPreferredStyleOverlayDonor : NSObject
+@end
+
+@implementation FakeNSScrollerPreferredStyleOverlayDonor
+
++ (NSInteger)preferredScrollerStyle {
+  return NSScrollerStyleOverlay;
+}
+
+@end
+
+namespace ui {
+namespace test {
+
+ScopedPreferredScrollerStyle::ScopedPreferredScrollerStyle(bool overlay)
+    : overlay_(overlay) {
+  if (![NSScroller respondsToSelector:@selector(preferredScrollerStyle)])
+    return;
+
+  NSInteger previous_style = [NSScroller preferredScrollerStyle];
+  Class style_class = overlay_
+                          ? [FakeNSScrollerPreferredStyleOverlayDonor class]
+                          : [FakeNSScrollerPreferredStyleLegacyDonor class];
+
+  swizzler_.reset(new ScopedObjCClassSwizzler(
+      [NSScroller class], style_class, @selector(preferredScrollerStyle)));
+
+  if (previous_style != GetScrollerStyle(overlay_))
+    NotifyStyleChanged();
+}
+
+ScopedPreferredScrollerStyle::~ScopedPreferredScrollerStyle() {
+  if (!swizzler_)
+    return;  // Handle 10.6, which wouldn't have swizzled anything.
+
+  swizzler_.reset();
+
+  if ([NSScroller preferredScrollerStyle] != GetScrollerStyle(overlay_))
+    NotifyStyleChanged();
+}
+
+}  // namespace test
+}  // namespace ui