add a download slices table into history download db

components/history/core/browser/download_slice_info_unittest.cc

Index: components/history/core/browser/download_slice_info_unittest.cc
diff --git a/components/history/core/browser/download_slice_info_unittest.cc b/components/history/core/browser/download_slice_info_unittest.cc
new file mode 100644
index 0000000000000000000000000000000000000000..5a7f625558c21fc4ec3c0a8567e3d07ee7957e7a
--- /dev/null
+++ b/components/history/core/browser/download_slice_info_unittest.cc
@@ -0,0 +1,22 @@
+// 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 "download_slice_info.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace history {
+
+TEST(DownloadSliceInfoTest, CompareDownloadSliceInfo) {
+  DownloadSliceInfo info1(1, 500, 10);
+  DownloadSliceInfo info2(1, 500, 1000);
+  EXPECT_FALSE(info1 == info2);
+
+  info1.received_bytes = 1000;
+  EXPECT_TRUE(info1 == info2);
+
+  info1.offset = 1;
+  EXPECT_FALSE(info1 == info2);
+}
+
+}  // namespace history