Adds UMA metrics for renderer uptime

chrome/browser/metrics/renderer_uptime_web_contents_observer.h

Index: chrome/browser/metrics/renderer_uptime_web_contents_observer.h
diff --git a/chrome/browser/metrics/renderer_uptime_web_contents_observer.h b/chrome/browser/metrics/renderer_uptime_web_contents_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..d461882e79e8679e1a0b0f18df0a738fe7689f76
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+++ b/chrome/browser/metrics/renderer_uptime_web_contents_observer.h
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+// 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_WEB_CONTENTS_OBSERVER_H_
+#define CHROME_BROWSER_METRICS_RENDERER_UPTIME_WEB_CONTENTS_OBSERVER_H_
+
+#include "base/macros.h"
+#include "content/public/browser/web_contents_observer.h"
+#include "content/public/browser/web_contents_user_data.h"
+
+namespace metrics {
+
+// Observer for tracking web contents events.
+class RendererUptimeWebContentsObserver
+    : public content::WebContentsObserver,
+      public content::WebContentsUserData<RendererUptimeWebContentsObserver> {
+ public:
+  static RendererUptimeWebContentsObserver* CreateForWebContents(
+      content::WebContents* web_contents);
+
+ private:
+  friend class content::WebContentsUserData<RendererUptimeWebContentsObserver>;
+
+  explicit RendererUptimeWebContentsObserver(
+      content::WebContents* web_contents);
+
+  // content::WebContentsObserver:
+  void DocumentAvailableInMainFrame() override;
+
+  DISALLOW_COPY_AND_ASSIGN(RendererUptimeWebContentsObserver);
+};
+
+}  // namespace metrics
+
+#endif  // CHROME_BROWSER_METRICS_RENDERER_UPTIME_WEB_CONTENTS_OBSERVER_H_