Media Engagement: implement shell of the media engagement service.

chrome/browser/media/media_engagement_service.cc

+// 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.
+
+#include "chrome/browser/media/media_engagement_service.h"
+
+#include "chrome/browser/media/media_engagement_service_factory.h"
+#include "chrome/browser/profiles/profile.h"
+#include "content/public/browser/web_contents.h"
+#include "content/public/browser/web_contents_observer.h"
+#include "media/base/media_switches.h"
+
+class MediaEngagementService::ContentsObserver
+    : public content::WebContentsObserver {
+ public:
+  explicit ContentsObserver(content::WebContents* web_contents,

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

No explicit for 2 params.

[mlamouri (slow - plz ping), 2017/04/25 17:14:40]

Eh. As above :)

+                            MediaEngagementService* service)
+      : WebContentsObserver(web_contents), service_(service) {}
+
+  ~ContentsObserver() override = default;
+
+  // WebContentsObserver implementation.
+  void WebContentsDestroyed() override {
+    service_->contents_observers_.erase(this);
+    delete this;
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ContentsObserver);

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

last.

[mlamouri (slow - plz ping), 2017/04/25 17:14:40]

Done.

+
+  // |this| is owned by |service_|.
+  MediaEngagementService* service_;
+};
+
+// static
+bool MediaEngagementService::IsEnabled() {
+  return base::FeatureList::IsEnabled(media::kMediaEngagement);
+}
+
+// static
+MediaEngagementService* MediaEngagementService::Get(Profile* profile) {
+  DCHECK(IsEnabled());
+  return MediaEngagementServiceFactory::GetForProfile(profile);
+}
+
+// static
+void MediaEngagementService::CreateWebContentsObserver(
+    content::WebContents* web_contents) {
+  DCHECK(IsEnabled());
+  MediaEngagementService* service =
+      Get(Profile::FromBrowserContext(web_contents->GetBrowserContext()));
+  if (!service)
+    return;
+  service->contents_observers_.insert(
+      new ContentsObserver(web_contents, service));
+}
+
+MediaEngagementService::MediaEngagementService(Profile* profile) {
+  DCHECK(IsEnabled());
+}
+
+MediaEngagementService::~MediaEngagementService() = default;