[Downloads] Rework how hashes are calculated for download files.

content/public/browser/download_destination_observer.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 CONTENT_PUBLIC_BROWSER_DOWNLOAD_DESTINATION_OBSERVER_H_
-#define CONTENT_PUBLIC_BROWSER_DOWNLOAD_DESTINATION_OBSERVER_H_
-
-#include <stdint.h>
-
-#include <string>
-
-#include "content/public/browser/download_interrupt_reasons.h"
-
-namespace content {
-
-// Class that receives asynchronous events from a DownloadDestination about
-// downloading progress and completion.  These should report status when the
-// data arrives at its final location; i.e. DestinationUpdate should be
-// called after the destination is finished with whatever operation it
-// is doing on the data described by |bytes_so_far| and DestinationCompleted
-// should only be called once that is true for all data.
-//
-// All methods are invoked on the UI thread.
-//
-// Note that this interface does not deal with cross-thread lifetime issues.
-class DownloadDestinationObserver {
- public:
-  virtual void DestinationUpdate(int64_t bytes_so_far,
-                                 int64_t bytes_per_sec,
-                                 const std::string& hash_state) = 0;
-
-  virtual void DestinationError(DownloadInterruptReason reason) = 0;
-
-  virtual void DestinationCompleted(const std::string& final_hash) = 0;
-};
-
-}  // namespace content
-
-#endif  // CONTENT_PUBLIC_BROWSER_DOWNLOAD_DESTINATION_OBSERVER_H_