When the download folder does not exist, change the download folder to a user's "Downloads"

chrome/browser/download/base_file.h

 // Copyright (c) 2011 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 CHROME_BROWSER_DOWNLOAD_BASE_FILE_H_
 #define CHROME_BROWSER_DOWNLOAD_BASE_FILE_H_
 #pragma once
 
 #include <string>
 
@@ skipping 14 matching lines @@
 // for DownloadFile and SaveFile, which keep more state information.
 class BaseFile {
  public:
   BaseFile(const FilePath& full_path,
            const GURL& source_url,
            const GURL& referrer_url,
            int64 received_bytes,
            const linked_ptr<net::FileStream>& file_stream);
   virtual ~BaseFile();
 
-  // If calculate_hash is true, sha256 hash will be calculated.
-  bool Initialize(bool calculate_hash);
+  // If |calculate_hash| is true, sha256 hash will be calculated.
+  // If the file path is not decided yet (i.e. if we do not specify the
+  // file path when we create this BaseFile object), this method creates
+  // the file under |save_path|.
+  bool Initialize(bool calculate_hash, const FilePath& save_path);
 
   // Write a new chunk of data to the file. Returns true on success (all bytes
   // written to the file).
   bool AppendDataToFile(const char* data, size_t data_len);
 
   // Rename the download file. Returns true on success.
   virtual bool Rename(const FilePath& full_path);
 
   // Detach the file so it is not deleted on destruction.
   virtual void Detach();
@@ skipping 52 matching lines @@
   unsigned char sha256_hash_[kSha256HashLen];
 
   // Indicates that this class no longer owns the associated file, and so
   // won't delete it on destruction.
   bool detached_;
 
   DISALLOW_COPY_AND_ASSIGN(BaseFile);
 };
 
 #endif  // CHROME_BROWSER_DOWNLOAD_BASE_FILE_H_