Add more components_unittests to GN build

components/proxy_config/BUILD.gn

 # Copyright 2015 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.
 
 # GYP version: components/proxy_config.gypi:proxy_config_component
 component("proxy_config") {
   sources = [
     "proxy_config_dictionary.cc",
     "proxy_config_dictionary.h",
     "proxy_config_export.h",
     "proxy_prefs.cc",
     "proxy_prefs.h",
   ]
 
   defines = [ "PROXY_CONFIG_IMPLEMENTATION" ]
 
   deps = [
     "//base",
     "//net",
   ]
 }
+
+source_set("unit_tests") {
+  testonly = true
+  sources = [
+    "proxy_config_dictionary_unittest.cc",
+    "proxy_prefs_unittest.cc",
+  ]
+  deps = [
+    ":proxy_config",
+    "//testing/gtest",
+  ]
+}