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_legacy_mac.h"
+#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].
-@interface FakeNSScrollerPreferredStyleDonor : NSObject
+// Donates a testing implementation of +[NSScroller preferredScrollerStyle] by
+// returning NSScrollerStyleLegacy.
+@interface FakeNSScrollerPreferredStyleLegacyDonor : NSObject
 @end
 
-@implementation FakeNSScrollerPreferredStyleDonor
+@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 {
 
-ScopedPreferredScrollerStyleLegacy::ScopedPreferredScrollerStyleLegacy() {
+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],
-                                  [FakeNSScrollerPreferredStyleDonor class],
+                                  style_class,
                                   @selector(preferredScrollerStyle)));
 
-  if (previous_style != NSScrollerStyleLegacy)
+  if (previous_style != GetScrollerStyle(overlay_))
     NotifyStyleChanged();
 }
 
-ScopedPreferredScrollerStyleLegacy::~ScopedPreferredScrollerStyleLegacy() {
+ScopedPreferredScrollerStyle::~ScopedPreferredScrollerStyle() {
   if (!swizzler_)
     return;  // Handle 10.6, which wouldn't have swizzled anything.
 
   swizzler_.reset();
 
-  if ([NSScroller preferredScrollerStyle] != NSScrollerStyleLegacy)
+  if ([NSScroller preferredScrollerStyle] != GetScrollerStyle(overlay_))
     NotifyStyleChanged();
 }
 
 }  // namespace test
 }  // namespace ui