Fix issues and feature polishing for parallel download.

content/browser/download/parallel_download_utils.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 CONTENT_BROWSER_DOWNLOAD_PARALLEL_DOWNLOAD_UTILS_H_
 #define CONTENT_BROWSER_DOWNLOAD_PARALLEL_DOWNLOAD_UTILS_H_
 
 #include <vector>
 
 #include "content/browser/download/download_create_info.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/download_item.h"
 
 namespace content {
 
 // Return if the download should be a parallel download.
 CONTENT_EXPORT bool ShouldUseParallelDownload(
     const DownloadCreateInfo& create_info);
 
-// Return the slices to download for the remaining content.
-// This function chunks the content into slices.
+// Chunks the content that starts from |current_offset|, into at most
+// std::max(|request_count|, 1) smaller slices.
+// Each slice contains at least |min_slice_size| bytes unless |total_length|
+// is less than |min_slice_size|.
+// The last slice is half opened.
 CONTENT_EXPORT std::vector<DownloadItem::ReceivedSlice>
-FindSlicesForRemainingContent(int64_t bytes_received,
-                              int64_t content_length,
-                              int request_count);
+FindSlicesForRemainingContent(int64_t current_offset,
+                              int64_t total_length,
+                              int request_count,
+                              int64_t min_slice_size);
 
 // Given an array of slices that are received, returns an array of slices to
 // download. |received_slices| must be ordered by offsets.
 CONTENT_EXPORT std::vector<DownloadItem::ReceivedSlice> FindSlicesToDownload(
     const std::vector<DownloadItem::ReceivedSlice>& received_slices);
 
 // Adds or merges a new received slice into a vector of sorted slices. If the
 // slice can be merged with the slice preceding it, merge the 2 slices.
 // Otherwise, insert the slice and keep the vector sorted. Returns the index
 // of the newly updated slice.
@@ skipping 14 matching lines @@
 // Get the time delay to send parallel requests after the response of original
 // request is handled.
 CONTENT_EXPORT base::TimeDelta GetParallelRequestDelayConfig();
 
 // Print the states of received slices for debugging.
 CONTENT_EXPORT void DebugSlicesInfo(const DownloadItem::ReceivedSlices& slices);
 
 }  //  namespace content
 
 #endif  // CONTENT_BROWSER_DOWNLOAD_PARALLEL_DOWNLOAD_UTILS_H_