Add a utility function to calculate the next slice to download

content/browser/download/parallel_download_utils.h

Index: content/browser/download/parallel_download_utils.h
diff --git a/content/browser/download/parallel_download_utils.h b/content/browser/download/parallel_download_utils.h
new file mode 100644
index 0000000000000000000000000000000000000000..c76af1f8cd99cb4f09152d820c16f1143054c402
--- /dev/null
+++ b/content/browser/download/parallel_download_utils.h
@@ -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.
+
+#ifndef CONTENT_BROWSER_DOWNLOAD_PARALLEL_DOWNLOAD_UTILS_H_
+#define CONTENT_BROWSER_DOWNLOAD_PARALLEL_DOWNLOAD_UTILS_H_
+
+#include <vector>
+
+#include "content/public/browser/download_item.h"
+
+namespace content {
+
+// Find the first gap in an array of received slices and return it as the next
+// slice to download. If not found, return a slice that is to the end of all
+// slices. |received_slices| must be ordered by offsets.
+DownloadItem::ReceivedSlice FindNextSliceToDownload(
+    const std::vector<DownloadItem::ReceivedSlice>& received_slices);
+
+}  //  namespace content
+
+#endif  // CONTENT_BROWSER_DOWNLOAD_PARALLEL_DOWNLOAD_UTILS_H_