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

components/translate/core/browser/translate_script.cc

Index: components/translate/core/browser/translate_script.cc
diff --git a/components/translate/core/browser/translate_script.cc b/components/translate/core/browser/translate_script.cc
index 875fc7f45e3633100129b3a6e55b036f00295650..ca39852435ad0bd8668ddbb3b442682da7aa2969 100644
--- a/components/translate/core/browser/translate_script.cc
+++ b/components/translate/core/browser/translate_script.cc
@@ -61,6 +61,8 @@ TranslateScript::~TranslateScript() {
 }
 
 void TranslateScript::Request(const RequestCallback& callback) {
+  script_fetch_start_time_ = base::Time::Now().ToJsTime();
+
   DCHECK(data_.empty()) << "Do not fetch the script if it is already fetched";
   callback_list_.push_back(callback);
 
@@ -142,6 +144,9 @@ void TranslateScript::OnScriptFetchComplete(
     if (variations::GetVariationParams(kTranslateServerStudy, &params)) {
       server_params = params[kServerParams];
     }
+    base::StringAppendF(
+        &data_, "var gtTimeInfo = {'fetchStart': %f, 'fetchEnd': %f};\n",

[groby-ooo-7-16, 2016/08/18 22:35:04]

Question - wouldn't it make more sense to report just the delta? Or do we
actually need times?

[ftang, 2016/08/18 23:01:39]

I need time (at least one of them) so my js in the TranslateElement can
calculate the end-to-end latency by misusing the fetchStart. We also like to
know the delta between fetchStart and fetchEnd to see the fetch latency and also
factor out the effect by the browser cache. So... yes, we need time. 

+        script_fetch_start_time_, base::Time::Now().ToJsTime());
     base::StringAppendF(&data_, "var serverParams = '%s';\n",
                         server_params.c_str());