MacViews: Overlay Scrollbars with Show/Hide Animations

ui/views/cocoa/views_scrollbar_bridge.h

Index: ui/views/cocoa/views_scrollbar_bridge.h
diff --git a/ui/views/cocoa/views_scrollbar_bridge.h b/ui/views/cocoa/views_scrollbar_bridge.h
new file mode 100644
index 0000000000000000000000000000000000000000..eb070a161c572f7ecc6f4c31cb789bb559e6e8b4
--- /dev/null
+++ b/ui/views/cocoa/views_scrollbar_bridge.h
@@ -0,0 +1,40 @@
+// 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_VIEWS_COCOA_VIEWS_SCROLLBAR_BRIDGE_DELEGATE_H_
+#define UI_VIEWS_COCOA_VIEWS_SCROLLBAR_BRIDGE_DELEGATE_H_
+
+#import <Cocoa/Cocoa.h>
+
+#import "base/mac/scoped_nsobject.h"
+#include "ui/views/views_export.h"
+
+// The delegate set to ViewsScrollbarBridge.
+class ViewsScrollbarBridgeDelegate {
+ public:
+  // Invoked by ViewsScrollbarBridge when the system informs the process that
+  // the preferred scroller style has changed
+  virtual void OnScrollerStyleChanged() = 0;
+};
+
+// A bridge to NSScroller managed by NativeCocoaScrollbar. Serves as a helper
+// class to bridge NSScroller notifications and functions to CocoaScrollbar.
+@interface ViewsScrollbarBridge : NSObject {
+ @private
+  ViewsScrollbarBridgeDelegate* delegate_;  // Weak. Owns this.
+}
+
+// Initializes with the given delegate and registers for notifications on
+// scroller style changes.
+- (id)initWithDelegate:(ViewsScrollbarBridgeDelegate*)delegate;
+
+// Sets |delegate_| to nullptr.
+-(void)clearDelegate;
+
+// Returns the style of scrollers that OSX is using.
++ (NSScrollerStyle)getPreferredScrollerStyle;
+
+@end
+
+#endif