[DO NOT COMMIT] Re-use the dafsa code for s-w-r 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 "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.

[tyoshino (SeeGerritForStatus), 2015/11/04 08:34:07]

merge with the comments at L18-19?

[Adam Rice, 2015/11/05 05:30:39]

The FromGWS metrics are permanent, but the StaleWhileRevalidate ones should be
removed after 1 or 2 releases. To make it easy to remove, I'd rather not change
the comment above.

[tyoshino (SeeGerritForStatus), 2015/11/05 09:00:02]

Ah, got it!

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