[Downloads] Ask DownloadHistory if a download was from history.

chrome/browser/download/download_service.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_DOWNLOAD_DOWNLOAD_SERVICE_H_
 #define CHROME_BROWSER_DOWNLOAD_DOWNLOAD_SERVICE_H_
 
 #include "base/basictypes.h"
 #include "base/callback_forward.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 63 matching lines @@
   // ChromeDownloadManagerDelegate may be the target of callbacks from
   // the history service/DB thread and must be kept alive for those
   // callbacks.
   scoped_ptr<ChromeDownloadManagerDelegate> manager_delegate_;
 
   scoped_ptr<DownloadHistory> download_history_;
 
   // The UI controller is responsible for observing the download manager and
   // notifying the UI of any new downloads. Its lifetime matches that of the
   // associated download manager.
+  // Note on destruction order: download_ui_ depends on download_history_ and
+  // should be destroyed before the latter.
   scoped_ptr<DownloadUIController> download_ui_;
 
   // On Android, GET downloads are not handled by the DownloadManager.
   // Once we have extensions on android, we probably need the EventRouter
   // in ContentViewDownloadDelegate which knows about both GET and POST
   // downloads.
 #if !defined(OS_ANDROID)
   // The ExtensionDownloadsEventRouter dispatches download creation, change, and
   // erase events to extensions. Like ChromeDownloadManagerDelegate, it's a
   // chrome-level concept and its lifetime should match DownloadManager. There
   // should be a separate EDER for on-record and off-record managers.
   // There does not appear to be a separate ExtensionSystem for on-record and
   // off-record profiles, so ExtensionSystem cannot own the EDER.
   scoped_ptr<ExtensionDownloadsEventRouter> extension_event_router_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(DownloadService);
 };
 
 #endif  // CHROME_BROWSER_DOWNLOAD_DOWNLOAD_SERVICE_H_