Add precompiled headers to GN build for large targets.

extensions/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/crypto.gni")
 import("//build/config/features.gni")
 import("//extensions/extensions.gni")
 
 # GYP version: extensions/extensions.gyp:extensions_browser
 source_set("browser") {
@@ skipping 13 matching lines @@
     "//extensions/common",
     "//extensions/common/api",
     "//extensions/common/api:api_registration",
     "//extensions/strings",
     "//google_apis",
     "//skia",
     "//third_party/leveldatabase",
     "//third_party/re2",
   ]
 
-  # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
-  configs += [ "//build/config/compiler:no_size_t_to_int_warning" ]
+  configs += [
+    "//build/config:precompiled_headers",
+
+    # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
+    "//build/config/compiler:no_size_t_to_int_warning",
+  ]
 
   if (enable_extensions) {
     # Includes all API implementations and the ExtensionsApiClient
     # interface. Moving an API from src/chrome to src/extensions implies
     # it can be cleanly disabled with enable_extensions=false.
     # TODO: Eventually the entire extensions module should not be built
     # when enable_extensions=false.
     sources = rebase_path(extensions_gypi_values.extensions_browser_sources,
                           ".",
                           "//extensions")
@@ skipping 45 matching lines @@
           win_or_mac_sources = rebase_path(
                   extensions_gypi_values.extensions_browser_sources_win_or_mac,
                   ".",
                   "//extensions")
           sources += win_or_mac_sources
         }
       }
     }
   }
 }