Make the UI an observer of downloads.

content/browser/android/download_controller_android_impl.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.
 
 // This class pairs with DownloadController on Java side to forward requests
 // for GET downloads to the current DownloadListener. POST downloads are
 // handled on the native side.
 //
 // Both classes are Singleton classes. C++ object owns Java object.
 //
@@ skipping 58 matching lines @@
     // Default copy constructor is used for passing this struct by value.
   };
   struct JavaObject;
   friend struct DefaultSingletonTraits<DownloadControllerAndroidImpl>;
   DownloadControllerAndroidImpl();
   virtual ~DownloadControllerAndroidImpl();
 
   // DownloadControllerAndroid implementation.
   virtual void CreateGETDownload(RenderViewHost* source,
                                  int request_id) OVERRIDE;
-  virtual void OnPostDownloadStarted(WebContents* web_contents,
-                                     DownloadItem* download_item) OVERRIDE;
+  virtual void OnPostDownloadStarted(DownloadItem* download_item) OVERRIDE;
 
   // DownloadItem::Observer interface.
   virtual void OnDownloadUpdated(DownloadItem* item) OVERRIDE;
   virtual void OnDownloadOpened(DownloadItem* item) OVERRIDE;
 
 
   void PrepareDownloadInfo(const GlobalRequestID& global_id,
                            int render_process_id,
                            int render_view_id);
 
@@ skipping 27 matching lines @@
   JavaObject* GetJavaObject();
 
   JavaObject* java_object_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadControllerAndroidImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_ANDROID_DOWNLOAD_CONTROLLER_ANDROID_IMPL_H_