Add a NavigationThrottle to the public content/ interface

content/browser/frame_host/navigator_delegate.h

Index: content/browser/frame_host/navigator_delegate.h
diff --git a/content/browser/frame_host/navigator_delegate.h b/content/browser/frame_host/navigator_delegate.h
index ac8402c9f6e67021004f2b746041e381c6dcac23..b5b3d82c77ba2f45e1a862af09c568391ea37f38 100644
--- a/content/browser/frame_host/navigator_delegate.h
+++ b/content/browser/frame_host/navigator_delegate.h
@@ -41,6 +41,10 @@ class CONTENT_EXPORT NavigatorDelegate {
   // that |navigation_handle| will be destroyed at the end of this call.
   virtual void DidFinishNavigation(NavigationHandle* navigation_handle) {}
 
+  // Called when the network request is about to start to register the
+  // NavigationThrottles for the navigation.
+  virtual void AddNavigationThrottles(NavigationHandle* navigation_handle) {}
+
   // TODO(clamy): all methods below that are related to navigation
   // events should go away in favor of the ones above.