diff --git a/common/http_fetcher.h b/common/http_fetcher.h
index 11e8e9f..d2499eb 100644
--- a/common/http_fetcher.h
+++ b/common/http_fetcher.h
@@ -44,7 +44,7 @@
   // |proxy_resolver| is the resolver that will be consulted for proxy
   // settings. It may be null, in which case direct connections will
   // be used. Does not take ownership of the resolver.
-  HttpFetcher(ProxyResolver* proxy_resolver)
+  explicit HttpFetcher(ProxyResolver* proxy_resolver)
       : post_data_set_(false),
         http_response_code_(0),
         delegate_(nullptr),
@@ -95,6 +95,12 @@
   // TransferTerminated() will be called when the transfer is actually done.
   virtual void TerminateTransfer() = 0;
 
+  // Add or update a custom header to be sent with every request. If the same
+  // |header_name| is passed twice, the second |header_value| would override the
+  // previous value.
+  virtual void SetHeader(const std::string& header_name,
+                         const std::string& header_value) = 0;
+
   // If data is coming in too quickly, you can call Pause() to pause the
   // transfer. The delegate will not have ReceivedBytes() called while
   // an HttpFetcher is paused.