New TimeToFirstURLJob* navigation metrics now work with PlzNavigate.

content/browser/loader/navigation_url_loader_delegate.h

 // Copyright 2014 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_BROWSER_LOADER_NAVIGATION_URL_LOADER_DELEGATE_H_
 #define CONTENT_BROWSER_LOADER_NAVIGATION_URL_LOADER_DELEGATE_H_
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 21 matching lines @@
   // made to the delegate. The response body is returned as a stream in
   // |body_stream|.
   virtual void OnResponseStarted(
       const scoped_refptr<ResourceResponse>& response,
       scoped_ptr<StreamHandle> body_stream) = 0;
 
   // Called if the request fails before receving a response. |net_error| is a
   // network error code for the failure.
   virtual void OnRequestFailed(int net_error) = 0;
 
+  // Called right before the first navigation network request happens, providing
+  // the |timestamp| when that happened in the IO thread.
+  virtual void AboutToBeginNavigation(base::TimeTicks timestamp) = 0;
+
  protected:
   NavigationURLLoaderDelegate() {}
   virtual ~NavigationURLLoaderDelegate() {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(NavigationURLLoaderDelegate);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_LOADER_NAVIGATION_URL_LOADER_DELEGATE_H_