Fix history importing by delaying DownloadManager creation.

content/browser/download/download_id_factory.h

+// Copyright (c) 2011 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 CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_ID_FACTORY_H_
+#define CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_ID_FACTORY_H_
+#pragma once
+
+#include "base/memory/ref_counted.h"
+#include "base/synchronization/lock.h"
+#include "content/browser/download/download_id.h"
+#include "content/public/browser/browser_thread.h"
+
+class DownloadManager;
+
+class CONTENT_EXPORT DownloadIdFactory
+    : public base::RefCountedThreadSafe<DownloadIdFactory> {
+ public:
+  // TODO(benjhayden): Instantiate with an explicit next id counter read from
+  // persistent storage.
+  DownloadIdFactory(DownloadId::Domain domain);
+
+  DownloadId GetNextId();
+
+ private:
+  DownloadId::Domain domain_;
+  int next_id_;
+  base::Lock lock_;
+
+  DISALLOW_COPY_AND_ASSIGN(DownloadIdFactory);
+};
+
+#endif  // CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_ID_FACTORY_H_