Prevent tracking metrics for cases such as 204s and downloads.

content/public/browser/navigation_handle.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_PUBLIC_BROWSER_NAVIGATION_HANDLE_H_
 #define CONTENT_PUBLIC_BROWSER_NAVIGATION_HANDLE_H_
 
 #include <memory>
 
 #include "content/common/content_export.h"
@@ skipping 141 matching lines @@
   // successful commits or error pages that replace the previous page
   // (distinguished by |IsErrorPage|), and false for errors that leave the user
   // on the previous page.
   virtual bool HasCommitted() = 0;
 
   // Whether the navigation resulted in an error page.
   // Note that if an error page reloads, this will return true even though
   // GetNetErrorCode will be net::OK.
   virtual bool IsErrorPage() = 0;
 
-  // Returns the response headers for the request or nullptr if there are none.
-  // This should only be accessed after a redirect was encountered or after the
-  // navigation is ready to commit. The headers returned should not be modified,
-  // as modifications will not be reflected in the network stack.
+  // Returns the response headers for the request, or nullptr if there aren't
+  // any response headers or they have not been received yet. The response
+  // headers may change during the navigation (e.g. after encountering a server
+  // redirect). The headers returned should not be modified, as modifications
+  // will not be reflected in the network stack.
   virtual const net::HttpResponseHeaders* GetResponseHeaders() = 0;
 
   // Resumes a navigation that was previously deferred by a NavigationThrottle.
   virtual void Resume() = 0;
 
   // Cancels a navigation that was previously deferred by a NavigationThrottle.
   // |result| should be equal to NavigationThrottle::CANCEL or
   // NavigationThrottle::CANCEL_AND_IGNORE.
   virtual void CancelDeferredNavigation(
       NavigationThrottle::ThrottleCheckResult result) = 0;
@@ skipping 44 matching lines @@
 
   // The NavigationData that the embedder returned from
   // ResourceDispatcherHostDelegate::GetNavigationData during commit. This will
   // be a clone of the NavigationData.
   virtual NavigationData* GetNavigationData() = 0;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_NAVIGATION_HANDLE_H_