Plumb experiment flags through page_load_metrics and add a new observer

components/page_load_metrics/renderer/page_timing_metrics_sender.cc

 // Copyright 2015 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/page_load_metrics/renderer/page_timing_metrics_sender.h"
 
 #include <utility>
 
 #include "base/callback.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
 #include "components/page_load_metrics/common/page_load_metrics_messages.h"
 #include "ipc/ipc_sender.h"
 
 namespace page_load_metrics {
 
 namespace {
 const int kTimerDelayMillis = 1000;
 }  // namespace
 
 PageTimingMetricsSender::PageTimingMetricsSender(IPC::Sender* ipc_sender,
                                                  int routing_id,
                                                  scoped_ptr<base::Timer> timer)
     : ipc_sender_(ipc_sender),
       routing_id_(routing_id),
-      timer_(std::move(timer)) {}
+      timer_(std::move(timer)),
+      metadata_(PageLoadMetadata()) {}
 
 // On destruction, we want to send any data we have if we have a timer
 // currently running (and thus are talking to a browser process)
 PageTimingMetricsSender::~PageTimingMetricsSender() {
   if (timer_->IsRunning()) {
     timer_->Stop();
     SendNow();
   }
 }
 
+void PageTimingMetricsSender::DidUseExperiment(blink::WebExperimentData data) {
+  metadata_.experiment_flags |= data;
+}
+
 void PageTimingMetricsSender::Send(const PageLoadTiming& timing) {
   if (timing == last_timing_)
     return;
 
   // We want to make sure that each PageTimingMetricsSender is associated
   // with a distinct page navigation. Because we reset the object on commit,
   // we can trash last_timing_ on a provisional load before SendNow() fires.
   if (!last_timing_.navigation_start.is_null() &&
       last_timing_.navigation_start != timing.navigation_start) {
     return;
   }
 
   last_timing_ = timing;
 
   if (!timer_->IsRunning())
     timer_->Start(
         FROM_HERE, base::TimeDelta::FromMilliseconds(kTimerDelayMillis),
         base::Bind(&PageTimingMetricsSender::SendNow, base::Unretained(this)));
 }
 
 void PageTimingMetricsSender::SendNow() {
-  ipc_sender_->Send(
-      new PageLoadMetricsMsg_TimingUpdated(routing_id_, last_timing_));
+  ipc_sender_->Send(new PageLoadMetricsMsg_TimingUpdated(
+      routing_id_, last_timing_, metadata_));
 }
 
 }  // namespace page_load_metrics