Adds UMA metrics for renderer uptime

chrome/browser/metrics/renderer_uptime_tracker.h

+// 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.
+
+#ifndef CHROME_BROWSER_METRICS_RENDERER_UPTIME_TRACKER_H_
+#define CHROME_BROWSER_METRICS_RENDERER_UPTIME_TRACKER_H_
+
+#include <map>
+
+#include "base/time/time.h"
+#include "content/public/browser/notification_observer.h"
+#include "content/public/browser/notification_registrar.h"
+
+// Class for tracking and renderer uptime info.
+class RendererUptimeTracker : public content::NotificationObserver {
+ public:
+  // Creates the |RendererUptimeTracker| instance and initializes the
+  // observers that notify to it.
+  static void Initialize();

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

Where is this called? I think it should be called early during start up - so
that you register for notifications early and don't miss anything.

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

The first RenderProcessHost instances seem to be created in
PreMainMessageLoopRun so I would like to call this before that. I have placed it
next to DesktopSessionDurationTracker::Initialize().

+
+  // Returns true if the |RendererUptimeTracker| instance has been
+  // created.
+  static bool IsInitialized();

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

Any reason to have this since there's already a Get() function?

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

Sorry. Removed.

+
+  // Returns the |RendererUptimeTracker| instance.
+  static RendererUptimeTracker* Get();
+
+  void OnRendererStarted(int pid);
+  void OnRendererTerminated(int pid);
+  void OnLoadInMainFrame(int pid);

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

These can now be private, right?

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

Done. Moved private methods to private.

+
+  // content::NotificationObserver:
+  void Observe(int type,
+               const content::NotificationSource& source,
+               const content::NotificationDetails& details) override;
+
+ protected:
+  RendererUptimeTracker();
+  ~RendererUptimeTracker() override;
+
+  struct RendererInfo {
+    base::TimeTicks launched_at_;
+    int num_loads_;
+    int num_loads_in_main_frame_;
+  };
+
+ private:
+  // Object for registering notification requests.
+  content::NotificationRegistrar registrar_;
+
+  // Maps RenderProcessHost ID to its info on uptime.
+  std::map<int, RendererInfo> info_map_;
+
+  DISALLOW_COPY_AND_ASSIGN(RendererUptimeTracker);
+};
+
+#endif  // CHROME_BROWSER_METRICS_RENDERER_UPTIME_TRACKER_H_