Add subresource filter page load metrics observer

chrome/test/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//chrome/common/features.gni")
@@ skipping 3223 matching lines @@
     "../browser/page_load_metrics/observers/data_reduction_proxy_metrics_observer_unittest.cc",
     "../browser/page_load_metrics/observers/document_write_page_load_metrics_observer_unittest.cc",
     "../browser/page_load_metrics/observers/from_gws_page_load_metrics_observer_unittest.cc",
     "../browser/page_load_metrics/observers/google_captcha_observer_unittest.cc",
     "../browser/page_load_metrics/observers/page_load_metrics_observer_test_harness.cc",
     "../browser/page_load_metrics/observers/page_load_metrics_observer_test_harness.h",
     "../browser/page_load_metrics/observers/previews_page_load_metrics_observer_unittest.cc",
     "../browser/page_load_metrics/observers/protocol_page_load_metrics_observer_unittest.cc",
     "../browser/page_load_metrics/observers/resource_prefetch_predictor_page_load_metrics_observer_unittest.cc",
     "../browser/page_load_metrics/observers/service_worker_page_load_metrics_observer_unittest.cc",
+    "../browser/page_load_metrics/observers/subresource_filter_metrics_observer_unittest.cc",
     "../browser/page_load_metrics/observers/ukm_page_load_metrics_observer_unittest.cc",
     "../browser/page_load_metrics/user_input_tracker_unittest.cc",
     "../browser/password_manager/chrome_password_manager_client_unittest.cc",
     "../browser/password_manager/password_manager_internals_service_unittest.cc",
     "../browser/password_manager/password_store_mac_unittest.cc",
     "../browser/password_manager/password_store_proxy_mac_unittest.cc",
     "../browser/password_manager/password_store_win_unittest.cc",
     "../browser/password_manager/password_store_x_unittest.cc",
     "../browser/password_manager/simple_password_store_mac_unittest.cc",
     "../browser/permissions/chooser_context_base_unittest.cc",
@@ skipping 1921 matching lines @@
 }
 
 if (is_win) {
   loadable_module("conflicts_dll") {
     testonly = true
     sources = [
       "conflicts/conflicts_dll.cc",
     ]
   }
 }