Tracing for NavigationHandle lifetime and state.

content/public/browser/navigation_throttle.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_THROTTLE_H_
 #define CONTENT_PUBLIC_BROWSER_NAVIGATION_THROTTLE_H_
 
 #include "content/common/content_export.h"
 
 namespace content {
@@ skipping 59 matching lines @@
   // Called when a response's headers and metadata are available.
   //
   // The implementer is responsible for ensuring that the WebContents this
   // throttle is associated with remain alive during the duration of this
   // method. Failing to do so will result in use-after-free bugs. Should the
   // implementer need to destroy the WebContents, it should return CANCEL,
   // CANCEL_AND_IGNORE, or BLOCK_RESPONSE and perform the destruction
   // asynchronously.
   virtual ThrottleCheckResult WillProcessResponse();
 
+  // Returns the name of the throttle for logging purposes. It must not return
+  // nullptr.
+  virtual const char* GetNameForLogging();

[clamy, 2017/04/24 12:30:22]

Should we make this pure virtual to ensure that implementers of
NavigationThrottles set it? I'm worried that some will forget to define it,
leading to less useful traces. For the record, that's the approach taken by the
ResourceThrottle.

[nasko, 2017/04/24 14:06:39]

Yes. Meant to, but missed it. Thanks!

+
   // The NavigationHandle that is tracking the information related to this
   // navigation.
   NavigationHandle* navigation_handle() const { return navigation_handle_; }
 
  private:
   NavigationHandle* navigation_handle_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_NAVIGATION_THROTTLE_H_