Notify page load metrics when the app enters the background.

chrome/browser/metrics/page_load_metrics_provider.cc

+// 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.
+
+#include "chrome/browser/metrics/page_load_metrics_provider.h"
+
+#include <vector>
+
+#include "chrome/browser/page_load_metrics/metrics_web_contents_observer.h"
+
+PageLoadMetricsProvider::PageLoadMetricsProvider() {}
+
+PageLoadMetricsProvider::~PageLoadMetricsProvider() {}
+
+void PageLoadMetricsProvider::OnAppEnterBackground() {
+  std::vector<page_load_metrics::MetricsWebContentsObserver*> observers =
+      page_load_metrics::MetricsWebContentsObserver::GetAllObservers();
+  for (auto observer : observers) {

[Charlie Harrison, 2016/07/28 14:45:27]

I would prefer if iterating through all MWCO happens here, instead of on a
static method on MWCO.

[Bryan McQuade, 2016/07/28 16:26:11]

See later comment - I think I'm inclined to move the
WebContentsImpl::GetAllWebContents to a public header that can be used by code
in chrome/. If we decide not to do that, I'd like to keep this method in a
header so I can test it (as I've done in our browsertest). I could move it to
page_load_metrics_provider.h but that feels like a stranger place for that
method to live than the MWCO header.

+    observer->FlushMetricsOnAppEnterBackground();
+  }
+}