Move the logic to determine how much data can be written to another function

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 165 matching lines @@
 
   // Rename file_ based on |parameters|.
   void RenameWithRetryInternal(std::unique_ptr<RenameParameters> parameters);
 
   // Send an update on our progress.
   void SendUpdate();
 
   // Called before the data is written to disk.
   void WillWriteToDisk(size_t data_len);
 
+  // For a given SourceStream object and the bytes it has read, determine the
+  // actual number of bytes it can write to the disk. For parallel downloading,
+  // if the first disk IO writes to a location that is already written by
+  // another stream, the current stream should stop writing. Returns true if the
+  // stream can write no more data and should be finished, returns false
+  // otherwise.
+  bool CalculateBytesToWrite(SourceStream* source_stream,
+                             size_t bytes_read,
+                             size_t* bytes_to_write);
+
   // Called when there's some activity on the byte stream that needs to be
   // handled.
   void StreamActive(SourceStream* source_stream);
 
   // Register callback and start to read data from the stream.
   void RegisterAndActivateStream(SourceStream* source_stream);
 
   // Adds a new slice to |received_slices_| and update the existing entries in
   // |source_streams_| as their lengths will change.
   // TODO(qinmin): add a test for this function.
@@ skipping 45 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_