Add component for feature engagement tracking.

components/feature_engagement_tracker/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")
+}
+
+group("feature_engagement_tracker") {
+  public_deps = [
+    "//components/feature_engagement_tracker/public",
+  ]
+
+  deps = [
+    "//components/feature_engagement_tracker/internal",
+  ]
+}
+
+group("unit_tests") {
+  testonly = true
+
+  deps = [
+    "//components/feature_engagement_tracker/internal:unit_tests",
+  ]
+}
+
+if (is_android) {
+  java_group("feature_engagement_tracker_java") {
+    deps = [
+      "//components/feature_engagement_tracker/internal:internal_java",
+      "//components/feature_engagement_tracker/public:public_java",
+    ]
+  }
+}