Tracing for NavigationHandle lifetime and state.

content/public/browser/navigation_throttle.h

Index: content/public/browser/navigation_throttle.h
diff --git a/content/public/browser/navigation_throttle.h b/content/public/browser/navigation_throttle.h
index 109a2fc4760f79c66796aa76b14fc135b3e07301..1c89b222e83ed7761b3f73550b1253854317629d 100644
--- a/content/public/browser/navigation_throttle.h
+++ b/content/public/browser/navigation_throttle.h
@@ -77,6 +77,10 @@ class CONTENT_EXPORT NavigationThrottle {
   // 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_; }