Add precompiled headers to GN build for large targets.

chrome/browser/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/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//third_party/protobuf/proto_library.gni")
 
@@ skipping 42 matching lines @@
   # are just itself and common gnome ones we link already, so we can get away
   # with additionally just coding the library name here.
   config("gnome_keyring_direct") {
     libs = [ "gnome-keyring" ]
   }
 }
 
 source_set("browser") {
   configs += [
     "//build/config/compiler:wexit_time_destructors",
+    "//build/config:precompiled_headers",
     "//third_party/WebKit/public:debug_devtools",
   ]
   defines = []
   sources = []
   libs = []
   ldflags = []
 
   # iOS/non-iOS shared deps. New dependencies should generally be added in the
   # non-iOS deps below.
   public_deps = [
@@ skipping 953 matching lines @@
     "ssl/ssl_client_auth_requestor_mock.cc",
     "ssl/ssl_client_auth_requestor_mock.h",
     "sync/profile_sync_components_factory_mock.cc",
     "sync/profile_sync_components_factory_mock.h",
     "sync/profile_sync_service_mock.cc",
     "sync/profile_sync_service_mock.h",
     "ui/webui/signin/login_ui_test_utils.cc",
     "ui/webui/signin/login_ui_test_utils.h",
   ]
 
+  configs += [ "//build/config:precompiled_headers" ]
+
   public_deps = [
     ":browser",
     "//chrome/browser/ui:test_support",
   ]
   deps = [
     "//base:prefs_test_support",
     "//chrome/browser",
     "//chrome/common",
     "//chrome/common/safe_browsing:proto",
     "//components/invalidation/impl",
@@ skipping 158 matching lines @@
         rebase_path(gypi_values.chrome_browser_rlz_sources, ".", "//chrome")
     deps = [
       "//components/google/core/browser",
       "//components/omnibox/browser",
       "//components/rlz",
       "//components/search_engines",
       "//rlz:rlz_lib",
     ]
   }
 }