New TimeToFirstURLJob* navigation metrics now work with PlzNavigate.

content/browser/frame_host/navigator.h

 // Copyright 2013 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_FRAME_HOST_NAVIGATOR_H_
 #define CONTENT_BROWSER_FRAME_HOST_NAVIGATOR_H_
 
 #include "base/memory/ref_counted.h"
 #include "base/time/time.h"
 #include "content/common/content_export.h"
@@ skipping 120 matching lines @@
   // response to the navigation request has been received).
   virtual void CommitNavigation(FrameTreeNode* frame_tree_node,
                                 ResourceResponse* response,
                                 scoped_ptr<StreamHandle> body);
 
   // PlzNavigate
   // Cancel a NavigationRequest for |frame_tree_node|. Called when
   // |frame_tree_node| is destroyed.
   virtual void CancelNavigation(FrameTreeNode* frame_tree_node) {}
 
-  // Called when the first resource request for a given navigation is executed
-  // so that it can be tracked into an histogram.
+  // Called when the network stack started handling the navigation request
+  // so that the |timestamp| when it happened can be recorded into an histogram.
+  // The |url| is used to verify we're tracking the correct navigation.
+  // TODO(carlosk): once PlzNavigate is the only navigation implementation
+  // remove the URL parameter and rename this method to better suit its naming
+  // conventions.
   virtual void LogResourceRequestTime(
     base::TimeTicks timestamp, const GURL& url) {};
 
   // Called to record the time it took to execute the before unload hook for the
   // current navigation.
   virtual void LogBeforeUnloadTime(
       const base::TimeTicks& renderer_before_unload_start_time,
       const base::TimeTicks& renderer_before_unload_end_time) {}
 
   // PlzNavigate
   // Returns whether there is an ongoing navigation waiting for the BeforeUnload
   // event to execute in the renderer process.
   virtual bool IsWaitingForBeforeUnloadACK(FrameTreeNode* frame_tree_node);
 
  protected:
   friend class base::RefCounted<Navigator>;
   virtual ~Navigator() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_FRAME_HOST_NAVIGATOR_H_