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

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

 // 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.
 
 #include "chrome/browser/ui/cocoa/download/download_item_mac.h"
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/download/download_item_model.h"
@@ skipping 53 matching lines @@
 
 void DownloadItemMac::OnDownloadDestroyed(content::DownloadItem* download) {
   [item_controller_ remove];  // We're deleted now!
 }
 
 void DownloadItemMac::OnDownloadOpened(content::DownloadItem* download) {
   DCHECK_EQ(download, download_model_.download());
   [item_controller_ downloadWasOpened];
 }
 
+void DownloadItemMac::OnDownloadShown(content::DownloadItem* download) {
+  DCHECK_EQ(download, download_model_.download());
+  [item_controller_ downloadWasShown];
+}
+
 void DownloadItemMac::LoadIcon() {
   IconManager* icon_manager = g_browser_process->icon_manager();
   if (!icon_manager) {
     NOTREACHED();
     return;
   }
 
   // We may already have this particular image cached.
   base::FilePath file = download_model_.download()->GetTargetFilePath();
   gfx::Image* icon = icon_manager->LookupIconFromFilepath(
       file, IconLoader::ALL);
   if (icon) {
     [item_controller_ setIcon:icon->ToNSImage()];
     return;
   }
 
   // The icon isn't cached, load it asynchronously.
   icon_manager->LoadIcon(file,
                          IconLoader::ALL,
                          base::Bind(&DownloadItemMac::OnExtractIconComplete,
                                     base::Unretained(this)),
                          &cancelable_task_tracker_);
 }
 
 void DownloadItemMac::OnExtractIconComplete(gfx::Image* icon) {
   if (!icon)
     return;
   [item_controller_ setIcon:icon->ToNSImage()];
 }