add a download slices table into history download db

components/history/core/browser/download_slice_info.cc

+// 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.
+
+#include "components/history/core/browser/download_slice_info.h"
+
+#include "components/history/core/browser/download_constants.h"
+
+namespace history {
+
+DownloadSliceInfo::DownloadSliceInfo()
+    : download_id(kInvalidDownloadId),
+      offset(0),
+      received_bytes(0) {}
+
+DownloadSliceInfo::DownloadSliceInfo(DownloadId download_id,
+                                     int64_t offset,
+                                     int64_t received_bytes)
+    : download_id(download_id),
+      offset(offset),
+      received_bytes(received_bytes) {}
+
+DownloadSliceInfo::DownloadSliceInfo(const DownloadSliceInfo& other) = default;
+
+DownloadSliceInfo::~DownloadSliceInfo() = default;
+
+bool DownloadSliceInfo::operator==(const DownloadSliceInfo& rhs) const {
+  return download_id == rhs.download_id && offset == rhs.offset &&
+      received_bytes == rhs.received_bytes;
+}
+
+}  // namespace history