Download shelf autohides on showing in shell, just same as regular open

chrome/browser/ui/cocoa/download/download_item_mac.h

 // Copyright (c) 2012 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 CHROME_BROWSER_UI_COCOA_DOWNLOAD_DOWNLOAD_ITEM_MAC_H_
 #define CHROME_BROWSER_UI_COCOA_DOWNLOAD_DOWNLOAD_ITEM_MAC_H_
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/macros.h"
@@ skipping 17 matching lines @@
  public:
   DownloadItemMac(content::DownloadItem* download,
                   DownloadItemController* controller);
 
   // Destructor.
   ~DownloadItemMac() override;
 
   // content::DownloadItem::Observer implementation
   void OnDownloadUpdated(content::DownloadItem* download) override;
   void OnDownloadOpened(content::DownloadItem* download) override;
+  void OnDownloadShown(content::DownloadItem* download) override;
   void OnDownloadDestroyed(content::DownloadItem* download) override;
 
   DownloadItemModel* download_model() { return &download_model_; }
 
   // Asynchronous icon loading support.
   void LoadIcon();
 
  private:
   // Callback for asynchronous icon loading.
   void OnExtractIconComplete(gfx::Image* icon_bitmap);
 
   // The download item model we represent.
   DownloadItemModel download_model_;
 
   // The objective-c controller object.
   DownloadItemController* item_controller_;  // weak, owns us.
 
   // For canceling an in progress icon request.
   base::CancelableTaskTracker cancelable_task_tracker_;
 
   // Stores the last known path where the file will be saved.
   base::FilePath lastFilePath_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadItemMac);
 };
 
 #endif  // CHROME_BROWSER_UI_COCOA_DOWNLOAD_DOWNLOAD_ITEM_MAC_H_