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

content/public/browser/download_save_info.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_SAVE_INFO_H_
 #define CONTENT_PUBLIC_BROWSER_DOWNLOAD_SAVE_INFO_H_
 
 #include <stdint.h>
 
 #include "base/files/file.h"
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "content/common/content_export.h"
+#include "crypto/secure_hash.h"
 
 namespace content {
 
 // Holds the information about how to save a download file.
 // In the case of download continuation, |file_path| is set to the current file
 // name, |offset| is set to the point where we left off, and |hash_state| will
 // hold the state of the hash algorithm where we left off.
 struct CONTENT_EXPORT DownloadSaveInfo {
   DownloadSaveInfo();
   ~DownloadSaveInfo();
+  DownloadSaveInfo(DownloadSaveInfo&& that);
 
   // If non-empty, contains the full target path of the download that has been
   // determined prior to download initiation. This is considered to be a trusted
   // path.
   base::FilePath file_path;
 
   // If non-empty, contains an untrusted filename suggestion. This can't contain
   // a path (only a filename), and is only effective if |file_path| is empty.
   base::string16 suggested_name;
 
   // If valid, contains the source data stream for the file contents.
   base::File file;
 
   // The file offset at which to start the download.  May be 0.
   int64_t offset;
 
-  // The state of the hash at the start of the download.  May be empty.
-  std::string hash_state;
+  // The state of the hash. If specified, this hash state must indicate the
+  // state of the partial file for the first |offset| bytes.
+  scoped_ptr<crypto::SecureHash> hash_state;
+
+  // SHA-256 hash of the first |offset| bytes of the file. Only used if |offset|
+  // is non-zero and either |file_path| or |file| specifies the file which
+  // contains the |offset| number of bytes. Can be empty, in which case no
+  // verification is done on the existing file.
+  std::string hash_of_partial_file;
 
   // If |prompt_for_save_location| is true, and |file_path| is empty, then
   // the user will be prompted for a location to save the download. Otherwise,
   // the location will be determined automatically using |file_path| as a
   // basis if |file_path| is not empty.
   // |prompt_for_save_location| defaults to false.
   bool prompt_for_save_location;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(DownloadSaveInfo);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_DOWNLOAD_SAVE_INFO_H_