Add component for feature engagement tracking.

chrome/browser/feature_engagement_tracker/feature_engagement_tracker_factory.h

Index: chrome/browser/feature_engagement_tracker/feature_engagement_tracker_factory.h
diff --git a/chrome/browser/feature_engagement_tracker/feature_engagement_tracker_factory.h b/chrome/browser/feature_engagement_tracker/feature_engagement_tracker_factory.h
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+// 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_FEATURE_ENGAGEMENT_TRACKER_FEATURE_ENGAGEMENT_TRACKER_FACTORY_H_
+#define CHROME_BROWSER_FEATURE_ENGAGEMENT_TRACKER_FEATURE_ENGAGEMENT_TRACKER_FACTORY_H_
+
+#include "base/macros.h"
+#include "components/keyed_service/content/browser_context_keyed_service_factory.h"
+
+namespace base {
+template <typename T>
+struct DefaultSingletonTraits;
+}  // namespace base
+
+namespace content {
+class BrowserContext;
+}  // namespace content
+
+namespace feature_engagement_tracker {
+class FeatureEngagementTracker;
+}  // namespace feature_engagement_tracker
+
+// FeatureEngagementTrackerFactory is the main client class for interaction with
+// the feature_engagement_tracker component.
+class FeatureEngagementTrackerFactory
+    : public BrowserContextKeyedServiceFactory {
+ public:
+  // Returns singleton instance of FeatureEngagementTrackerFactory.
+  static FeatureEngagementTrackerFactory* GetInstance();
+
+  // Returns the FeatureEngagementTracker associated with |context|.
+  static feature_engagement_tracker::FeatureEngagementTracker*
+  GetForBrowserContext(content::BrowserContext* context);
+
+ private:
+  friend struct base::DefaultSingletonTraits<FeatureEngagementTrackerFactory>;
+
+  FeatureEngagementTrackerFactory();
+  ~FeatureEngagementTrackerFactory() override;
+
+  // BrowserContextKeyedServiceFactory overrides:
+  KeyedService* BuildServiceInstanceFor(
+      content::BrowserContext* context) const override;
+  content::BrowserContext* GetBrowserContextToUse(
+      content::BrowserContext* context) const override;
+
+  DISALLOW_COPY_AND_ASSIGN(FeatureEngagementTrackerFactory);
+};
+
+#endif  // CHROME_BROWSER_FEATURE_ENGAGEMENT_TRACKER_FEATURE_ENGAGEMENT_TRACKER_FACTORY_H_