Add precompiled headers to GN build for large targets.

chrome/browser/ui/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("//build/config/ui.gni")
 
 gypi_values = exec_script("//build/gypi_to_gn.py",
                           [ rebase_path("../../chrome_browser_ui.gypi") ],
                           "scope",
                           [ "../../chrome_browser_ui.gypi" ])
 
 source_set("ui") {
   output_name = "browser_ui"
 
   sources = []
   defines = []
   libs = []
 
   configs += [
+    "//build/config:precompiled_headers",
     "//build/config/compiler:wexit_time_destructors",
     "//third_party/WebKit/public:debug_devtools",
   ]
 
   # Since browser and browser_ui actually depend on each other,
   # we must omit the dependency from browser_ui to browser.
   # However, this means browser_ui and browser should more or less
   # have the same dependencies. Once browser_ui is untangled from
   # browser, then we can clean up these dependencies.
   public_deps = [
@@ skipping 495 matching lines @@
     "//chrome/browser",
     "//content/public/browser",
     "//content/public/common",
     "//content/test:test_support",
     "//net:test_support",
     "//skia",
     "//testing/gtest",
     "//ui/base",
   ]
 }