Make the UI an observer of downloads.

chrome/browser/download/download_ui_controller.h

+// Copyright 2013 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_UI_CONTROLLER_H_
+#define CHROME_BROWSER_DOWNLOAD_DOWNLOAD_UI_CONTROLLER_H_
+
+#include <set>
+
+#include "base/memory/scoped_ptr.h"
+#include "chrome/browser/download/all_download_item_notifier.h"
+
+class Profile;
+
+namespace content {
+class WebContents;
+}
+
+// This class handles the task of observing for download notifications and
+// notifying the UI when a new download should be displayed in the UI.
+//
+// This class monitors each IN_PROGRESS download that is created (for which
+// OnDownloadCreated is called) until:
+// - it is assigned a target path or
+// - is interrupted.
+// Then the NotifyDownloadStarting() method of the Delegate is invoked.
+class DownloadUIController : public AllDownloadItemNotifier::Observer {
+ public:
+  // The delegate is responsible for figuring out how to notify the UI.
+  class Delegate {
+   public:
+    virtual ~Delegate();
+    virtual void NotifyDownloadStarting(content::DownloadItem* item) = 0;
+  };
+
+  // |manager| is the download manager to observe for new downloads. If
+  // |delegate.get()| is NULL, then the default delegate is constructed.
+  //
+  // On Android the default delegate notifies DownloadControllerAndroid. On
+  // other platforms the target of the notification is a Browser object.
+  //
+  // Currently explicit delegates are only used for testing.
+  DownloadUIController(content::DownloadManager* manager,
+                       scoped_ptr<Delegate> delegate);
+
+  virtual ~DownloadUIController();
+
+ private:
+  virtual void OnDownloadCreated(content::DownloadManager* manager,
+                                 content::DownloadItem* item) OVERRIDE;
+  virtual void OnDownloadUpdated(content::DownloadManager* manager,
+                                 content::DownloadItem* item) OVERRIDE;
+
+  AllDownloadItemNotifier download_notifier_;
+
+  scoped_ptr<Delegate> delegate_;
+
+  DISALLOW_COPY_AND_ASSIGN(DownloadUIController);
+};
+
+#endif  // CHROME_BROWSER_DOWNLOAD_DOWNLOAD_UI_CONTROLLER_H_