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

chrome/browser/page_load_metrics/observers/stale_while_revalidate_metrics_observer.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/observers/stale_while_revalidate_metrics_observer.h"
+
+#include "components/page_load_metrics/browser/page_load_metrics_macros.h"
+#include "components/page_load_metrics/common/page_load_timing.h"
+#include "net/base/swr_histogram_domains/swr_histogram_domains.h"
+
+StaleWhileRevalidateMetricsObserver::StaleWhileRevalidateMetricsObserver(
+    page_load_metrics::PageLoadMetricsObservable* metrics)
+    : is_interesting_domain_(false), metrics_(metrics) {}
+
+void StaleWhileRevalidateMetricsObserver::OnCommit(
+    content::NavigationHandle* navigation_handle) {
+  is_interesting_domain_ =
+      net::swr_histogram_domains::IsHostInSWRHistogramDomain(
+          navigation_handle->GetURL().host());
+}
+
+void StaleWhileRevalidateMetricsObserver::OnComplete(
+    const page_load_metrics::PageLoadTiming& timing,
+    const page_load_metrics::PageLoadExtraInfo& extra_info) {
+  if (!is_interesting_domain_)
+    return;
+
+  if (!timing.load_event_start.is_zero()) {
+    PAGE_LOAD_HISTOGRAM(
+        "PageLoad.Clients.StaleWhileRevalidateExperiment.Timing2."
+        "NavigationToLoadEventFired",
+        timing.load_event_start);
+  }
+  if (!timing.first_layout.is_zero()) {
+    PAGE_LOAD_HISTOGRAM(
+        "PageLoad.Clients.StaleWhileRevalidateExperiment.Timing2."
+        "NavigationToFirstLayout",
+        timing.first_layout);
+  }
+  if (!timing.first_text_paint.is_zero()) {
+    PAGE_LOAD_HISTOGRAM(
+        "PageLoad.Clients.StaleWhileRevalidateExperiment.Timing2."
+        "NavigationToFirstTextPaint",
+        timing.first_text_paint);
+  }
+}
+
+void StaleWhileRevalidateMetricsObserver::OnPageLoadMetricsGoingAway() {
+  metrics_->RemoveObserver(this);
+  delete this;
+}