New histogram to track overhead time spent around beforeunload event + fixes

content/browser/frame_host/navigator_impl.cc

 // 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.
 
 #include "content/browser/frame_host/navigator_impl.h"
 
 #include "base/command_line.h"
 #include "base/metrics/histogram.h"
 #include "base/time/time.h"
 #include "content/browser/frame_host/frame_tree.h"
@@ skipping 869 matching lines @@
 
   base::TimeDelta time_to_commit =
       base::TimeTicks::Now() - navigation_data_->start_time_;
   UMA_HISTOGRAM_TIMES("Navigation.TimeToCommit", time_to_commit);
 
   time_to_commit -= navigation_data_->before_unload_delay_;
   base::TimeDelta time_to_network = navigation_data_->url_job_start_time_ -
                                     navigation_data_->start_time_ -
                                     navigation_data_->before_unload_delay_;
   if (navigation_data_->is_restoring_from_last_session_) {
-    DCHECK(!navigation_data_->before_unload_delay_.InMicroseconds());
     UMA_HISTOGRAM_TIMES(
         "Navigation.TimeToCommit_SessionRestored",
         time_to_commit);
     UMA_HISTOGRAM_TIMES(
         "Navigation.TimeToURLJobStart_SessionRestored",
         time_to_network);
     navigation_data_.reset();
     return;
   }
   RenderProcessHostImpl* process_host =
@@ skipping 12 matching lines @@
         "Navigation.TimeToCommit_ExistingRenderer_BeforeUnloadDiscounted",
         time_to_commit);
     UMA_HISTOGRAM_TIMES(
         "Navigation.TimeToURLJobStart_ExistingRenderer_BeforeUnloadDiscounted",
         time_to_network);
   }
   navigation_data_.reset();
 }
 
 }  // namespace content