Add time from navigation_start to NTP LogEvent

chrome/browser/ui/webui/ntp/ntp_user_data_logger.h

Index: chrome/browser/ui/webui/ntp/ntp_user_data_logger.h
diff --git a/chrome/browser/ui/webui/ntp/ntp_user_data_logger.h b/chrome/browser/ui/webui/ntp/ntp_user_data_logger.h
index e723c697899f52c7a5f59538860594a2356e0539..b31c9980b4427edf8e6d0aad21177060f0861d4f 100644
--- a/chrome/browser/ui/webui/ntp/ntp_user_data_logger.h
+++ b/chrome/browser/ui/webui/ntp/ntp_user_data_logger.h
@@ -41,9 +41,10 @@ class NTPUserDataLogger
   // the tab/shutting down Chrome), or when the user navigates to a URL.
   void EmitNtpStatistics();
 
-  // Called each time an event occurs on the NTP that requires a counter to be
-  // incremented.
-  void LogEvent(NTPLoggingEventType event);
+  // Called when an event occurs on the NTP that requires a counter to be
+  // incremented. |time| is the delta time in ms from navigation start until
+  // this event happened.
+  void LogEvent(NTPLoggingEventType event, uint64 time);

[James Hawkins, 2015/03/19 20:10:07]

Why not use TimeDelta?

https://code.google.com/p/chromium/codesearch#chromium/src/base/time/time.h&q...

[fserb, 2015/03/19 20:15:30]

so... the problem is we are constructing this time from the difference from
NavigationStart which is created as a TimeDelta, but then saved as an int64
since epoch on the renderer. And it's not trivial to do the reverse operation
without some weird hacking. If you look at searchbox.cc on this CL you will see
what I mean.

I can still convert the timestamp that I generate with
TimeDelta.fromMilliseconds(...) if you'd prefer like that.

 
   // Logs an impression on one of the Most Visited tiles by a given provider.
   void LogMostVisitedImpression(int position, const base::string16& provider);