chrome: Cleanup class/struct forward declarations

chrome/browser/safe_browsing/incident_reporting/download_metadata_manager.h

 // Copyright 2014 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_SAFE_BROWSING_INCIDENT_REPORTING_DOWNLOAD_METADATA_MANAGER_H_
 #define CHROME_BROWSER_SAFE_BROWSING_INCIDENT_REPORTING_DOWNLOAD_METADATA_MANAGER_H_
 
 #include <map>
 #include <memory>
 
 #include "base/callback_forward.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "content/public/browser/download_manager.h"
 
 namespace base {
 class SequencedTaskRunner;
 class SequencedWorkerPool;
 }
 
 namespace content {
 class BrowserContext;
 class DownloadItem;
 }
 
 namespace safe_browsing {
 
 class ClientDownloadRequest;
 class ClientIncidentReport_DownloadDetails;
-class DownloadMetadata;
 
 // A browser-wide object that manages the persistent state of metadata
 // pertaining to a download.
 class DownloadMetadataManager : public content::DownloadManager::Observer {
  public:
   // A callback run when the results of a call to GetDownloadDetails are ready.
   // The supplied parameter may be null, indicating that there are no persisted
   // details for the |browser_context| passed to GetDownloadDetails.
   typedef base::Callback<void(
       std::unique_ptr<ClientIncidentReport_DownloadDetails>)>
@@ skipping 51 matching lines @@
   // Contexts for each DownloadManager that has been added and has not yet
   // "gone down".
   ManagerToContextMap contexts_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadMetadataManager);
 };
 
 }  // namespace safe_browsing
 
 #endif  // CHROME_BROWSER_SAFE_BROWSING_INCIDENT_REPORTING_DOWNLOAD_METADATA_MANAGER_H_