Add a PersistentStore to FeatureEngagementTracker

components/feature_engagement_tracker/internal/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")
 }
 
 static_library("internal") {
@@ skipping 18 matching lines @@
     "in_memory_store.h",
     "model.h",
     "model_impl.cc",
     "model_impl.h",
     "never_condition_validator.cc",
     "never_condition_validator.h",
     "never_storage_validator.cc",
     "never_storage_validator.h",
     "once_condition_validator.cc",
     "once_condition_validator.h",
+    "persistent_store.cc",
+    "persistent_store.h",
     "single_invalid_configuration.cc",
     "single_invalid_configuration.h",
     "storage_validator.h",
     "store.h",
     "system_time_provider.cc",
     "system_time_provider.h",
     "time_provider.h",
   ]
 
   public_deps = [
     "//components/feature_engagement_tracker/internal/proto",
   ]
 
   deps = [
     "//base",
     "//components/feature_engagement_tracker/public",
     "//components/keyed_service/core",
+    "//components/leveldb_proto",
   ]
 
   if (is_android) {
     sources += [
       "android/feature_engagement_tracker_impl_android.cc",
       "android/feature_engagement_tracker_impl_android.h",
       "android/feature_engagement_tracker_jni_registrar.cc",
     ]
 
     deps += [ ":jni_headers" ]
@@ skipping 11 matching lines @@
     "chrome_variations_configuration_unittest.cc",
     "configuration_unittest.cc",
     "editable_configuration_unittest.cc",
     "feature_config_storage_validator_unittest.cc",
     "feature_engagement_tracker_impl_unittest.cc",
     "in_memory_store_unittest.cc",
     "model_impl_unittest.cc",
     "never_condition_validator_unittest.cc",
     "never_storage_validator_unittest.cc",
     "once_condition_validator_unittest.cc",
+    "persistent_store_unittest.cc",
     "single_invalid_configuration_unittest.cc",
     "system_time_provider_unittest.cc",
   ]
 
   deps = [
     ":internal",
     "//base/test:test_support",
+    "//components/feature_engagement_tracker/internal/test:test_support",
+    "//components/leveldb_proto:test_support",
     "//testing/gtest",
   ]
 }
 
 if (is_android) {
   android_library("internal_java") {
     visibility = [ "//components/feature_engagement_tracker:feature_engagement_tracker_java" ]
 
     java_files = [ "android/java/src/org/chromium/components/feature_engagement_tracker/internal/FeatureEngagementTrackerImpl.java" ]
 
     deps = [
       "//base:base_java",
       "//components/feature_engagement_tracker/public:public_java",
     ]
   }
 
   generate_jni("jni_headers") {
     visibility = [ ":*" ]
     sources = [
       "android/java/src/org/chromium/components/feature_engagement_tracker/internal/FeatureEngagementTrackerImpl.java",
     ]
     jni_package = "components/feature_engagement_tracker/internal"
   }
 }