Adds UMA metrics for renderer uptime

chrome/browser/metrics/renderer_uptime_web_contents_observer.cc

+// Copyright 2017 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/renderer_uptime_web_contents_observer.h"
+
+#include "chrome/browser/metrics/renderer_uptime_tracker.h"
+#include "content/public/browser/render_process_host.h"
+
+DEFINE_WEB_CONTENTS_USER_DATA_KEY(metrics::RendererUptimeWebContentsObserver);
+
+namespace metrics {
+
+RendererUptimeWebContentsObserver::RendererUptimeWebContentsObserver(
+    content::WebContents* web_contents)
+    : content::WebContentsObserver(web_contents) {}
+
+// static
+RendererUptimeWebContentsObserver*
+RendererUptimeWebContentsObserver::CreateForWebContents(
+    content::WebContents* web_contents) {
+  DCHECK(web_contents);
+
+  if (!RendererUptimeTracker::IsInitialized())
+    return nullptr;
+
+  RendererUptimeWebContentsObserver* observer = FromWebContents(web_contents);
+  if (!observer) {
+    observer = new RendererUptimeWebContentsObserver(web_contents);
+    web_contents->SetUserData(UserDataKey(), observer);
+  }
+  return observer;
+}
+
+void RendererUptimeWebContentsObserver::DocumentAvailableInMainFrame() {
+  if (!RendererUptimeTracker::IsInitialized())
+    return;
+  ::RendererUptimeTracker::Get()->OnLoadInMainFrame(

[Alexei Svitkine (slow), 2017/03/01 15:50:18]

Nit: No ::

[keishi, 2017/03/02 09:37:14]

Done.

+      web_contents()->GetRenderProcessHost()->GetID());
+}
+
+}  // namespace metrics