Add StaleWhileRevalidateExperiment histograms.

chrome/browser/page_load_metrics/page_load_metrics_initialize.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 "chrome/browser/page_load_metrics/page_load_metrics_initialize.h"
 
 #include "chrome/browser/page_load_metrics/observers/from_gws_page_load_metrics_observer.h"
+#include "chrome/browser/page_load_metrics/observers/stale_while_revalidate_metrics_observer.h"
 #include "components/page_load_metrics/browser/metrics_web_contents_observer.h"
 #include "components/rappor/rappor_service.h"
 #include "content/public/browser/web_contents.h"
 
 namespace {
 
 void RegisterPageLoadMetricsObservers(
     page_load_metrics::PageLoadMetricsObservable* metrics) {
   // Attach observers scoped to the web contents here.
 
   // This is a self-destruct class, and will delete itself when triggered by
   // OnPageLoadMetricsGoingAway.
   metrics->AddObserver(new FromGWSPageLoadMetricsObserver(metrics));
+  // StaleWhileRevalidateMetricsObserver also deletes itself from
+  // OnPageLoadMetricsGoingAway.
+  // TODO(ricea): Remove this in January 2016 or before.

[kinuko, 2015/11/17 08:18:48]

nit: do you have an umbrella bug for the experiment? Would be nice to have a
link to crbug in general

[Adam Rice, 2015/11/17 18:29:20]

I don't have a bug for the experiments. I have added a reference to the feature
bug which I have updated with notes about the experiments I plan to do.

+  metrics->AddObserver(
+      new chrome::StaleWhileRevalidateMetricsObserver(metrics));
 }
 
 }  // namespace
 
 namespace chrome {
 
 void InitializePageLoadMetricsForWebContents(
     content::WebContents* web_contents,
     rappor::RapporService* rappor_service) {
   RegisterPageLoadMetricsObservers(
       page_load_metrics::MetricsWebContentsObserver::CreateForWebContents(
           web_contents, rappor_service));
 }
 
 }  // namespace chrome