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

chrome/browser/download/base_file.h

Index: chrome/browser/download/base_file.h
diff --git a/chrome/browser/download/base_file.h b/chrome/browser/download/base_file.h
index 02563b7e6b92deb0f93dba96a9a178d75577188f..ab7cb323105dfd2d098d8214e0c510d0fa03ed2d 100644
--- a/chrome/browser/download/base_file.h
+++ b/chrome/browser/download/base_file.h
@@ -32,8 +32,11 @@ class BaseFile {
            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).