AU: Push seeks in http fetching to the progress percentage.

http_fetcher.h

Index: http_fetcher.h
diff --git a/http_fetcher.h b/http_fetcher.h
index f61116a1dc05ad762bf7d3a7f7eccc56ef0e5551..d0f9cb207ad4d72ee9f0fd9f8b5caa0a8c19d965 100644
--- a/http_fetcher.h
+++ b/http_fetcher.h
@@ -89,12 +89,14 @@ class HttpFetcher {
 // Interface for delegates
 class HttpFetcherDelegate {
  public:
-  // Called every time bytes are received, even if they are automatically
-  // delivered to an output file.
+  // Called every time bytes are received.
   virtual void ReceivedBytes(HttpFetcher* fetcher,
                              const char* bytes,
                              int length) = 0;
 
+  // Called if the fetcher seeks to a particular offset.
+  virtual void SeekToOffset(off_t offset) {}
+
   // Called when the transfer has completed successfully or been somehow
   // aborted.
   virtual void TransferComplete(HttpFetcher* fetcher, bool successful) = 0;