Add a PersistentStore to FeatureEngagementTracker

components/feature_engagement_tracker/internal/test/BUILD.gn

Index: components/feature_engagement_tracker/internal/test/BUILD.gn
diff --git a/components/feature_engagement_tracker/internal/test/BUILD.gn b/components/feature_engagement_tracker/internal/test/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..5715c47377d402c27b611636b12e4a0991deb456
--- /dev/null
+++ b/components/feature_engagement_tracker/internal/test/BUILD.gn
@@ -0,0 +1,22 @@
+# 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.
+
+source_set("test_support") {
+  testonly = true
+
+  visibility = [ "//components/feature_engagement_tracker/internal:unit_tests" ]
+
+  sources = [
+    "event_util.cc",
+    "event_util.h",
+  ]
+
+  public_deps = [
+    "//components/feature_engagement_tracker/internal/proto",
+  ]
+
+  deps = [
+    "//testing/gtest",
+  ]
+}