Add precompiled headers to GN build for large targets.

base/test/BUILD.gn

 # Copyright (c) 2013 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/ui.gni")
 
 if (is_android) {
   import("//build/config/android/rules.gni")
 }
 
@@ skipping 106 matching lines @@
     "trace_event_analyzer.cc",
     "trace_event_analyzer.h",
     "trace_to_file.cc",
     "trace_to_file.h",
     "user_action_tester.cc",
     "user_action_tester.h",
     "values_test_util.cc",
     "values_test_util.h",
   ]
 
+  configs += [ "//build/config:precompiled_headers" ]
+
   data = [
     # The isolate needs this script for setting up the test. It's not actually
     # needed to run this target locally.
     "//testing/test_env.py",
   ]
 
   public_deps = [
     ":test_config",
     "//base",
     "//base:i18n",
@@ skipping 70 matching lines @@
 
 if (is_android) {
   generate_jni("base_unittests_jni_headers") {
     sources = [
       "android/java/src/org/chromium/base/ContentUriTestUtils.java",
       "android/java/src/org/chromium/base/TestUiThread.java",
     ]
     jni_package = "base"
   }
 }