Add component for feature engagement tracking.

components/feature_engagement_tracker/public/BUILD.gn

+# 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.
+
+if (is_android) {
+  import("//build/config/android/config.gni")
+  import("//build/config/android/rules.gni")
+}
+
+source_set("public") {
+  visibility = [ "*" ]
+
+  sources = [
+    "feature_engagement_tracker.h",
+  ]
+
+  deps = [
+    "//base",
+    "//components/keyed_service/core",
+  ]
+
+  if (is_android) {
+    sources += [ "android/feature_engagement_tracker_jni_registrar.h" ]
+  }
+}
+
+if (is_android) {
+  android_library("public_java") {
+    visibility = [ "*" ]
+
+    java_files = [ "android/java/src/org/chromium/components/feature_engagement_tracker/FeatureEngagementTracker.java" ]
+
+    deps = [
+      "//base:base_java",
+      "//third_party/android_tools:android_support_annotations_java",
+    ]
+  }
+}