pass script fetch start / end time to Transalte Element to implement real time latency monitoring

components/translate/core/browser/translate_script.h

Index: components/translate/core/browser/translate_script.h
diff --git a/components/translate/core/browser/translate_script.h b/components/translate/core/browser/translate_script.h
index 8c358735035d2328a38e4b79778078fd7fcff449..4454cdbcab449c6d93f41087f753b70bb4500d0a 100644
--- a/components/translate/core/browser/translate_script.h
+++ b/components/translate/core/browser/translate_script.h
@@ -80,6 +80,10 @@ class TranslateScript {
   // The JS injected in the page to do the translation.
   std::string data_;
 
+  // The starting time of fetching the translate script.
+  // Number of milliseconds since the epoch.
+  double script_fetch_start_time_;
+
   // Delay after which the translate script is fetched again from the translate
   // server.
   base::TimeDelta expiration_delay_;