MacViews: Overlay Scrollbars with Show/Hide Animations

ui/base/test/scoped_preferred_scroller_style_mac.h

 // 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.
 
 #ifndef UI_BASE_TEST_SCOPED_PREFERRED_SCROLLER_STYLE_LEGACY_MAC_H_
 #define UI_BASE_TEST_SCOPED_PREFERRED_SCROLLER_STYLE_LEGACY_MAC_H_
 
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 
 namespace base {
 namespace mac {
 class ScopedObjCClassSwizzler;
 }
 }
 
 namespace ui {
 namespace test {
 
-// Overrides system setting for scrollbar style with NSScrollerStyleLegacy,
-// which means "always show scrollbars".
-class ScopedPreferredScrollerStyleLegacy {
+// Overrides system setting for scrollbar style with NSScrollerOverlay if we
+// want the scrollbar to overlay. Otherwise, override with
+// NSScrollerStyleLegacy which means "always show scrollbars".
+class ScopedPreferredScrollerStyle {
  public:
-  ScopedPreferredScrollerStyleLegacy();
-  ~ScopedPreferredScrollerStyleLegacy();
+  explicit ScopedPreferredScrollerStyle(bool overlay);
+  ~ScopedPreferredScrollerStyle();
 
  private:
   scoped_ptr<base::mac::ScopedObjCClassSwizzler> swizzler_;
 
-  DISALLOW_COPY_AND_ASSIGN(ScopedPreferredScrollerStyleLegacy);
+  // True if the scrollbar style should overlay.
+  bool overlay_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedPreferredScrollerStyle);
 };
 
 }  // namespace test
 }  // namespace ui
 
 #endif  // UI_BASE_TEST_SCOPED_PREFERRED_SCROLLER_STYLE_LEGACY_MAC_H_