Add more components_unittests to GN build

components/error_page/renderer/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.
 
-static_library("renderer") {
+source_set("renderer") {
   sources = [
     "net_error_helper_core.cc",
     "net_error_helper_core.h",
   ]
 
   deps = [
     "//base",
     "//components/error_page/common",
     "//components/strings",
     "//components/url_formatter",
     "//content/public/common",
     "//net",
     "//third_party/WebKit/public:blink",
     "//ui/base",
     "//url",
   ]
 }
+
+source_set("unit_tests") {
+  testonly = true
+  sources = [
+    "net_error_helper_core_unittest.cc",
+  ]
+  deps = [
+    ":renderer",
+    "//testing/gtest",
+  ]
+}