Use ByteStream in downloads system to decouple source and sink.

content/browser/download/download_file.h

Index: content/browser/download/download_file.h
diff --git a/content/browser/download/download_file.h b/content/browser/download/download_file.h
index 0b1f5ffc26ea11de39667f2e1c40ae480ab4ecfb..cb30b2fa421423acd8b1998ccf04f93c6050597c 100644
--- a/content/browser/download/download_file.h
+++ b/content/browser/download/download_file.h
@@ -30,11 +30,6 @@ class CONTENT_EXPORT DownloadFile {
   // Returns net::OK on success, or a network error code on failure.
   virtual net::Error Initialize() = 0;
 
-  // Write a new chunk of data to the file.
-  // Returns net::OK on success (all bytes written to the file),
-  // or a network error code on failure.
-  virtual net::Error AppendDataToFile(const char* data, size_t data_len) = 0;
-
   // Rename the download file.
   // Returns net::OK on success, or a network error code on failure.
   virtual net::Error Rename(const FilePath& full_path) = 0;
@@ -45,9 +40,6 @@ class CONTENT_EXPORT DownloadFile {
   // Abort the download and automatically close the file.
   virtual void Cancel() = 0;
 
-  // Indicate that the download has finished. No new data will be received.
-  virtual void Finish() = 0;
-
   // Informs the OS that this file came from the internet.
   virtual void AnnotateWithSourceInformation() = 0;