AU: MultiHttpFetcher, an HttpFetcher for specific byte ranges

http_fetcher.h

Index: http_fetcher.h
diff --git a/http_fetcher.h b/http_fetcher.h
index f8e510a61d4c7fd241a8b3f28e0317eb9deea145..f61116a1dc05ad762bf7d3a7f7eccc56ef0e5551 100644
--- a/http_fetcher.h
+++ b/http_fetcher.h
@@ -42,6 +42,9 @@ class HttpFetcher {
     post_data_.insert(post_data_.end(), char_data, char_data + size);
   }
 
+  // Downloading should resume from this offset
+  virtual void SetOffset(off_t offset) = 0;
+
   // Begins the transfer to the specified URL.
   virtual void BeginTransfer(const std::string& url) = 0;
 
@@ -59,6 +62,11 @@ class HttpFetcher {
   // Unpause() returns
   virtual void Unpause() = 0;
 
+  // These two function are overloaded in LibcurlHttp fetcher to speed
+  // testing.
+  virtual void set_idle_seconds(int seconds) {}
+  virtual void set_retry_seconds(int seconds) {}
+
  protected:
   // The URL we're actively fetching from
   std::string url_;