Implement a basic Site Engagement Score service.

chrome/browser/engagement/site_engagement_helper.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 CHROME_BROWSER_ENGAGEMENT_SITE_ENGAGEMENT_HELPER_H_
+#define CHROME_BROWSER_ENGAGEMENT_SITE_ENGAGEMENT_HELPER_H_
+
+#include "base/macros.h"
+#include "content/public/browser/web_contents_observer.h"
+#include "content/public/browser/web_contents_user_data.h"
+
+namespace content {
+class WebContents;
+}
+
+class GURL;
+
+class SiteEngagementHelper

[raymes, 2015/04/16 01:13:55]

nit: Could you add a comment for this class?

[benwells, 2015/04/16 05:15:27]

Done.

+    : public content::WebContentsObserver,
+      public content::WebContentsUserData<SiteEngagementHelper> {
+ public:
+  ~SiteEngagementHelper() override;
+

[raymes, 2015/04/16 01:13:55]

nit: // WebContentsObserver overrides.

[benwells, 2015/04/16 05:15:27]

Done. I also made it private.

+  void DidStartNavigationToPendingEntry(
+      const GURL& url,
+      content::NavigationController::ReloadType reload_type) override;
+
+ private:
+  explicit SiteEngagementHelper(content::WebContents* web_contents);
+  friend class content::WebContentsUserData<SiteEngagementHelper>;
+
+  DISALLOW_COPY_AND_ASSIGN(SiteEngagementHelper);
+};
+
+#endif  // CHROME_BROWSER_ENGAGEMENT_SITE_ENGAGEMENT_HELPER_H_