Add a helper method to truncate SourceStream's length

content/browser/download/download_file_impl.h

 // Copyright (c) 2012 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_DOWNLOAD_FILE_IMPL_H_
 #define CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_FILE_IMPL_H_
 
 #include "content/browser/download/download_file.h"
 
 #include <stddef.h>
@@ skipping 88 matching lines @@
   class CONTENT_EXPORT SourceStream {
    public:
     SourceStream(int64_t offset,
                  int64_t length,
                  std::unique_ptr<ByteStreamReader> stream_reader);
     ~SourceStream();
 
     // Called after successfully writing a buffer to disk.
     void OnWriteBytesToDisk(int64_t bytes_write);
 
+    // Given a data block that is already written, truncate the length of this
+    // object to avoid overwriting that block.
+    void TruncateLengthWithWrittenDataBlock(int64_t offset,
+                                            int64_t bytes_written);
+
     ByteStreamReader* stream_reader() const { return stream_reader_.get(); }
     int64_t offset() const { return offset_; }
     int64_t length() const { return length_; }
     void set_length(int64_t length) { length_ = length; }
     int64_t bytes_written() const { return bytes_written_; }
     bool is_finished() const { return finished_; }
     void set_finished(bool finish) { finished_ = finish; }
     size_t index() { return index_; }
     void set_index(size_t index) { index_ = index; }
 
@@ skipping 145 matching lines @@
 
   base::WeakPtr<DownloadDestinationObserver> observer_;
   base::WeakPtrFactory<DownloadFileImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadFileImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_FILE_IMPL_H_