Adding histograms showing fraction of page load times

net/url_request/url_request_job.h

Index: net/url_request/url_request_job.h
===================================================================
--- net/url_request/url_request_job.h	(revision 148459)
+++ net/url_request/url_request_job.h	(working copy)
@@ -334,6 +334,9 @@
   // The default implementation does nothing.
   virtual void UpdatePacketReadTimes();
 
+  // Custom handler for derived classes when the request is detached.
+  virtual void OnDetachRequest() {}
+
   // Indicates that the job is done producing data, either it has completed
   // all the data or an error has been encountered. Set exclusively by
   // NotifyDone so that it is kept in sync with the request.