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

chrome/browser/ui/views/download/download_item_view.h

 // Copyright 2015 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.
 //
 // A view that implements one download on the Download shelf.
 // Each DownloadItemView contains an application icon, a text label
 // indicating the download's file name, a text label indicating the
 // download's status (such as the number of bytes downloaded so far)
 // and a button for canceling an in progress download, or opening
 // the completed download.
@@ skipping 69 matching lines @@
 
   // IconManager::Client interface.
   void OnExtractIconComplete(gfx::Image* icon);
 
   // Returns the DownloadItem model object belonging to this item.
   content::DownloadItem* download() { return model_.download(); }
 
   // DownloadItem::Observer methods
   void OnDownloadUpdated(content::DownloadItem* download) override;
   void OnDownloadOpened(content::DownloadItem* download) override;
+  void OnDownloadShown(content::DownloadItem* download) override;
   void OnDownloadDestroyed(content::DownloadItem* download) override;
 
   // Overridden from views::View:
   void Layout() override;
   gfx::Size GetPreferredSize() const override;
   bool OnMousePressed(const ui::MouseEvent& event) override;
   bool OnMouseDragged(const ui::MouseEvent& event) override;
   void OnMouseReleased(const ui::MouseEvent& event) override;
   void OnMouseCaptureLost() override;
   bool OnKeyPressed(const ui::KeyEvent& event) override;
@@ skipping 221 matching lines @@
   std::unique_ptr<extensions::ExperienceSamplingEvent> sampling_event_;
 
   // Method factory used to delay reenabling of the item when opening the
   // downloaded file.
   base::WeakPtrFactory<DownloadItemView> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadItemView);
 };
 
 #endif  // CHROME_BROWSER_UI_VIEWS_DOWNLOAD_DOWNLOAD_ITEM_VIEW_H_