Clear the received slices in DownloadItemImpl when etag changed.

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 cea23175752d648403c4a49729da452ced714430..224121a034b77a1073b4ec7923a1e9f6e94b83d4 100644
--- a/content/browser/download/download_file.h
+++ b/content/browser/download/download_file.h
@@ -14,6 +14,7 @@
 #include "base/files/file_path.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/download_interrupt_reasons.h"
+#include "content/public/browser/download_item.h"
 
 class GURL;
 
@@ -46,7 +47,9 @@ class CONTENT_EXPORT DownloadFile {
   // Upon completion, |callback| will be called on the UI
   // thread as per the comment above, passing DOWNLOAD_INTERRUPT_REASON_NONE
   // on success, or a network download interrupt reason on failure.
-  virtual void Initialize(const InitializeCallback& callback) = 0;
+  virtual void Initialize(
+      const InitializeCallback& callback,
+      const DownloadItem::ReceivedSlices& received_slices) = 0;
 
   // Add a byte stream reader to write into a slice of the file, used for
   // parallel download. Called on the file thread.