Media Engagement: implement shell of the media engagement service.

chrome/browser/media/media_engagement_service.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_MEDIA_MEDIA_ENGAGEMENT_SERVICE_H_
+#define CHROME_BROWSER_MEDIA_MEDIA_ENGAGEMENT_SERVICE_H_
+
+#include <set>
+
+#include "base/macros.h"
+#include "components/keyed_service/core/keyed_service.h"
+
+class Profile;
+
+namespace content {
+class WebContents;
+}  // namespace content
+
+class MediaEngagementService : public KeyedService {
+ public:
+  // Returns the instance attached to the given |profile|.
+  static MediaEngagementService* Get(Profile* profile);
+
+  // Returns whether the feature is enabled.
+  static bool IsEnabled();
+
+  // Observe the given |web_contents| by creating an internal
+  // WebContentsObserver.
+  static void CreateWebContentsObserver(content::WebContents* web_contents);
+
+  explicit MediaEngagementService(Profile* profile);
+  ~MediaEngagementService() override;
+
+ private:
+  class ContentsObserver;
+
+  std::set<ContentsObserver*> contents_observers_;
+
+  DISALLOW_COPY_AND_ASSIGN(MediaEngagementService);
+};
+
+#endif  // CHROME_BROWSER_MEDIA_MEDIA_ENGAGEMENT_SERVICE_H_