Add component for feature engagement tracking.

components/feature_engagement_tracker/internal/feature_engagement_tracker_impl.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 "components/feature_engagement_tracker/internal/feature_engagement_tracker_impl.h"
+
+namespace feature_engagement_tracker {
+
+// This method is declared in //components/feature_engagement_tracker/public/
+//     feature_engagement_tracker.h
+// and should be linked in to any binary using FeatureEngagementTracker::Create.
+// static
+FeatureEngagementTracker* FeatureEngagementTracker::Create(
+    const base::FilePath& storage_dir,
+    const scoped_refptr<base::SequencedTaskRunner>& background__task_runner) {
+  return new FeatureEngagementTrackerImpl;
+}
+
+FeatureEngagementTrackerImpl::FeatureEngagementTrackerImpl() = default;
+
+FeatureEngagementTrackerImpl::~FeatureEngagementTrackerImpl() = default;
+
+void FeatureEngagementTrackerImpl::Event(const std::string& feature,
+                                         const std::string& precondition) {
+  // TODO(nyquist): Track this event.
+}
+
+void FeatureEngagementTrackerImpl::Used(const std::string& feature) {
+  // TODO(nyquist): Track this event.
+}
+
+bool FeatureEngagementTrackerImpl::Trigger(const std::string& feature) {
+  // TODO(nyquist): Track this event and add business logic.
+  return false;
+}
+
+void FeatureEngagementTrackerImpl::Dismissed() {
+  // TODO(nyquist): Track this event.
+}
+
+void FeatureEngagementTrackerImpl::AddOnInitializedCallback(
+    OnInitializedCallback callback) {
+  // TODO(nyquist): Add support for this.
+}
+
+}  // namespace feature_engagement_tracker