Implement a basic Site Engagement Score service.

chrome/browser/engagement/site_engagement_service.h

Index: chrome/browser/engagement/site_engagement_service.h
diff --git a/chrome/browser/engagement/site_engagement_service.h b/chrome/browser/engagement/site_engagement_service.h
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+++ b/chrome/browser/engagement/site_engagement_service.h
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+// 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_SERVICE_H_
+#define CHROME_BROWSER_ENGAGEMENT_SITE_ENGAGEMENT_SERVICE_H_
+
+#include <map>
+
+#include "base/macros.h"
+#include "components/keyed_service/core/keyed_service.h"
+
+class GURL;
+class Profile;
+
+// Stores and retrieves the engagement score of an origin.
+//
+// An engagement score is a positive integer that represents how much a user has
+// engaged with an origin - the higher it is, the more engagement the user has
+// had with this site recently.
+//
+// Positive user activity, such as visiting the origin often and adding it to
+// the homescreen, will increase the site engagement score. Negative activity,
+// such as rejecting permission prompts or not responding to notifications, will
+// decrease the site engagement score.
+class SiteEngagementService : public KeyedService {
+ public:
+  static SiteEngagementService* Get(Profile* profile);
+
+  // Returns whether or not the SiteEngagementService is enabled.
+  static bool IsEnabled();
+
+  explicit SiteEngagementService(Profile* profile);
+  ~SiteEngagementService() override;
+
+  // Update the karma score of the origin matching |url| for user navigation.
+  void HandleNavigation(const GURL& url);
+
+  // Returns a non-negative integer representing the engagement score of the
+  // origin for this URL.
+  int GetScore(const GURL& url);
+
+ private:
+  Profile* profile_;
+
+  // Temporary non-persistent score database for testing.
+  std::map<GURL, int> scores_;
+
+  DISALLOW_COPY_AND_ASSIGN(SiteEngagementService);
+};
+
+#endif  // CHROME_BROWSER_ENGAGEMENT_SITE_ENGAGEMENT_SERVICE_H_