Sending the time of the pingback request in the request

components/data_reduction_proxy/proto/pageload_metrics.proto

 // Copyright 2016 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.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 
 import "client_config.proto";
 
 package data_reduction_proxy;
 
 // Request message to record metrics for one or more pageloads.
 message RecordPageloadMetricsRequest {
   // The pageload metrics to record.
   repeated PageloadMetrics pageloads = 1;
+  // Time metrics were sent.
+  optional Timestamp metrics_sent_time = 2;
 }
 
 // Metrics for a single pageload.
 message PageloadMetrics {
   // The session key used to load the page.
   optional string session_key = 1;
   // The time at which the first request of the pageload was made, according to
   // the client's clock.
   optional Timestamp first_request_time = 2;
   // The time at which the last request of the pageload was made, according to
@@ skipping 13 matching lines @@
   // Time to onLoad event.
   optional Duration page_load_time = 9;
 
   // The sum of original-content-length values, over resources that were not
   // loaded from browser cache.
   optional int32 original_page_size_bytes = 10;
   // The sum of (compressed) content-length, over resources that were not loaded
   // from browser cache.
   optional int32 compressed_page_size_bytes = 11;
 }