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

components/translate/core/browser/translate_script.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/translate/core/browser/translate_script.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/location.h"
 #include "base/logging.h"
@@ skipping 43 matching lines @@
 
 TranslateScript::TranslateScript()
     : expiration_delay_(base::TimeDelta::FromDays(kExpirationDelayDays)),
       weak_method_factory_(this) {
 }
 
 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);
 
   if (fetcher_.get() != NULL) {
     // If there is already a request in progress, do nothing. |callback| will be
     // run on completion.
     return;
   }
 
   GURL translate_script_url;
@@ skipping 61 matching lines @@
     data_ = base::StringPrintf("var translateApiKey = '%s';\n",
                                google_apis::GetAPIKey().c_str());
 
     // Insert server params to pass experimental params to google translate
     // server.
     std::string server_params;
     std::map<std::string, std::string> params;
     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());
 
     GURL security_origin = translate::GetTranslateSecurityOrigin();
     base::StringAppendF(
         &data_, "var securityOrigin = '%s';", security_origin.spec().c_str());
 
     // Append embedded translate.js and a remote element library.
     base::StringPiece str = ResourceBundle::GetSharedInstance().
         GetRawDataResource(IDR_TRANSLATE_JS);
@@ skipping 11 matching lines @@
 
   for (RequestCallbackList::iterator it = callback_list_.begin();
        it != callback_list_.end();
        ++it) {
     it->Run(success, data);
   }
   callback_list_.clear();
 }
 
 }  // namespace translate