Add precompiled headers to GN build for large targets.

sync/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/features.gni")
 import("//testing/test.gni")
 
 component("sync") {
   public_deps = [
     ":sync_core",
@@ skipping 388 matching lines @@
     "util/get_session_name_win.cc",
     "util/get_session_name_win.h",
     "util/logging.cc",
     "util/logging.h",
     "util/nigori.cc",
     "util/nigori.h",
     "util/time.cc",
     "util/time.h",
   ]
 
+  configs += [ "//build/config:precompiled_headers" ]
+
   public_deps = [
     "//sync/internal_api/attachments/proto",
   ]
   deps = [
     "//base",
     "//base:i18n",
     "//base/third_party/dynamic_annotations",
     "//crypto",
     "//google_apis",
     "//net",
@@ skipping 225 matching lines @@
     "syncable/syncable_id_unittest.cc",
     "syncable/syncable_unittest.cc",
     "syncable/syncable_util_unittest.cc",
     "util/cryptographer_unittest.cc",
     "util/data_type_histogram_unittest.cc",
     "util/get_session_name_unittest.cc",
     "util/nigori_unittest.cc",
     "util/protobuf_unittest.cc",
   ]
 
+  configs += [ "//build/config:precompiled_headers" ]
+
   deps = [
     ":test_support_sync_core",
     ":test_support_sync_internal_api",
     "//base",
     "//base/allocator",
     "//base/test:run_all_unittests",
     "//google_apis",
     "//google_apis:test_support",
     "//net",
     "//net:test_support",
@@ skipping 141 matching lines @@
       ":fake_server_jni",
       ":sync_core",
       ":test_support_sync_fake_server",
       "//base",
       "//sync/protocol:protocol",
       "//testing/gtest",
       "//url:url",
     ]
   }
 }