Add a function to add extra headers from NavigationThrottle

content/browser/frame_host/navigation_request_info.h

Index: content/browser/frame_host/navigation_request_info.h
diff --git a/content/browser/frame_host/navigation_request_info.h b/content/browser/frame_host/navigation_request_info.h
index f63db7738d3cbea252d2c2af181a62149346930b..85155b168cbe34d7095dc1870d7d9c3c5f40d7d5 100644
--- a/content/browser/frame_host/navigation_request_info.h
+++ b/content/browser/frame_host/navigation_request_info.h
@@ -32,7 +32,10 @@ struct CONTENT_EXPORT NavigationRequestInfo {
   ~NavigationRequestInfo();
 
   const CommonNavigationParams common_params;
-  const BeginNavigationParams begin_params;
+
+  // The headers may be changed by NavigationThrottles during calls to
+  // NavigationThrottle::WillStartRequest.
+  BeginNavigationParams begin_params;
 
   // Usually the URL of the document in the top-level window, which may be
   // checked by the third-party cookie blocking policy.