PageLoadMetrics renderer and browser implementation.

components/page_load_metrics/browser/metrics_web_contents_observer.h

+// 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.
+
+#ifndef COMPONENTS_PAGE_LOAD_METRICS_BROWSER_PAGE_LOAD_METRICS_WEB_CONTENTS_OBSERVER_H_
+#define COMPONENTS_PAGE_LOAD_METRICS_BROWSER_PAGE_LOAD_METRICS_WEB_CONTENTS_OBSERVER_H_
+
+#include "base/macros.h"
+#include "base/time/time.h"
+#include "components/page_load_metrics/common/page_load_timing.h"
+#include "content/public/browser/web_contents.h"
+#include "content/public/browser/web_contents_observer.h"
+#include "content/public/browser/web_contents_user_data.h"
+
+namespace content {
+class NavigationHandle;
+class RenderFrameHost;
+}  // namespace content
+
+namespace IPC {
+class Message;
+}  // namespace IPC
+
+namespace page_load_metrics {
+
+// MetricsWebContentsObserver logs page load UMA metrics based on
+// IPC messages received from a MainRenderFrameObserver.
+class MetricsWebContentsObserver
+    : public content::WebContentsObserver,
+      public content::WebContentsUserData<MetricsWebContentsObserver> {
+ public:
+  ~MetricsWebContentsObserver() override;
+
+  // WebContentsObserver implementation.

[Alexei Svitkine (slow), 2015/09/11 21:26:48]

Nit: For new code, I think this comment syntax is preferred:

// content::WebContentsObserver:

+  void FrameDeleted(content::RenderFrameHost* render_frame_host) override;
+  bool OnMessageReceived(const IPC::Message& message,
+                         content::RenderFrameHost* render_frame_host) override;
+  void DidCommitNavigation(
+      content::NavigationHandle* navigation_handle) override;
+  void RenderProcessGone(base::TerminationStatus status) override;
+
+ private:
+  explicit MetricsWebContentsObserver(content::WebContents* web_contents);
+  friend class content::WebContentsUserData<MetricsWebContentsObserver>;
+  friend class MetricsWebContentsObserverTest;
+
+  void OnTimingUpdated(content::RenderFrameHost*, const PageLoadTiming& timing);
+  void RecordTimingHistograms();
+
+  bool IsRelevantNavigation(content::NavigationHandle* navigation_handle);
+
+  content::RenderFrameHost* current_host_;
+
+  // Will be null before any navigations have committed. When a navigation
+  // commits we will initialize this as empty.
+  scoped_ptr<PageLoadTiming> current_timing_;
+
+  DISALLOW_COPY_AND_ASSIGN(MetricsWebContentsObserver);
+};
+
+}  // namespace page_load_metrics
+
+#endif  // COMPONENTS_PAGE_LOAD_METRICS_BROWSER_PAGE_LOAD_METRICS_WEB_CONTENTS_OBSERVER_H_