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 "components/keyed_service/core/keyed_service.h"
+
+class Profile;
+
+namespace content {
+class WebContents;
+}  // namespace content
+
+class MediaEngagementService : public KeyedService {

[DaleCurtis, 2017/04/25 16:57:59]

I thought we used namespaces in chrome/ now?

[mlamouri (slow - plz ping), 2017/04/25 17:14:41]

I do not remember hearing about this and code around uses namespace randomly
(`chrome`, specific, none). Do you have a preference? I don't apart that `media`
might clash with //media.

+ 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);
+
+  MediaEngagementService(Profile* profile);

[DaleCurtis, 2017/04/25 16:57:59]

explicit

[mlamouri (slow - plz ping), 2017/04/25 17:14:41]

We need automatic checks for these. Too easy to add/remove parameters and forget
:(

+  ~MediaEngagementService() override;
+
+ private:
+  class ContentsObserver;
+
+  std::set<ContentsObserver*> contents_observers_;

[DaleCurtis, 2017/04/25 16:57:59]

How many of these are expected? base::flat_set?

[mlamouri (slow - plz ping), 2017/04/25 17:14:41]

One per tab. I don't think flat_set is appropriate, from reading the doc.

+};

[DaleCurtis, 2017/04/25 16:57:59]

DISALLOW_COPY_AND_ASSIGN().

[mlamouri (slow - plz ping), 2017/04/25 17:14:41]

Done.

+
+#endif  // CHROME_BROWSER_MEDIA_MEDIA_ENGAGEMENT_SERVICE_H_