Adds a new UMA histogram to measure the NTP load time since navigation

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 30a03823871e3a3cc2290d24b930e8c7d7c45924..b31c09a516d6c5fe7c227d45cbc874b86c8f1db6 100644
--- a/chrome/browser/ui/webui/ntp/ntp_user_data_logger.h
+++ b/chrome/browser/ui/webui/ntp/ntp_user_data_logger.h
@@ -98,6 +98,12 @@ class NTPUserDataLogger
   // Total number of mouseovers for this NTP session.
   size_t number_of_mouseovers_;
 
+  // Time from navigation start it took to load the NTP in milliseconds.
+  base::TimeDelta load_time_;
+
+  // Whether we have already emitted NTP stats for this web contents.
+  bool has_emitted_;
+
   // The URL of this New Tab Page - varies based on NTP version.
   GURL ntp_url_;