add a download slices table into history download db

components/history/core/browser/download_slice_info.h

+// Copyright 2017 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 COMPONENTS_HISTORY_CORE_BROWSER_DOWNLOAD_SLICE_INFO_H_
+#define COMPONENTS_HISTORY_CORE_BROWSER_DOWNLOAD_SLICE_INFO_H_
+
+#include <stdint.h>
+#include <string>
+
+#include "components/history/core/browser/download_types.h"
+
+namespace history {
+
+// Contains the information for each slice of data that is written to the
+// download target file. A download file can have multiple slices and cach
+// slice will have a different offset.
+struct DownloadSliceInfo {
+  DownloadSliceInfo();
+  DownloadSliceInfo(DownloadId download_id,
+                    int64_t offset,
+                    int64_t received_bytes);
+  DownloadSliceInfo(const DownloadSliceInfo& other);
+  ~DownloadSliceInfo();
+
+  bool operator==(const DownloadSliceInfo&) const;
+
+  // The id of the download in the database.
+  DownloadId download_id;
+
+  // Start position of the download request.
+  int64_t offset;
+
+  // The number of bytes received (so far).
+  int64_t received_bytes;
+};
+
+}  // namespace history
+
+#endif  // COMPONENTS_HISTORY_CORE_BROWSER_DOWNLOAD_SLICE_INFO_H_