Add precompiled headers to GN build for large targets.

chrome/browser/devtools/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.
 
 if (!is_android) {
   import("//tools/grit/grit_rule.gni")
 }
 
 action("devtools_protocol_constants") {
   script = "devtools_protocol_constants_generator.py"
@@ skipping 34 matching lines @@
     "devtools_network_transaction_factory.cc",
     "devtools_network_transaction_factory.h",
     "devtools_protocol.cc",
     "devtools_protocol.h",
   ]
   sources += get_target_outputs(":devtools_protocol_constants")
 
   configs += [
     "//build/config/compiler:no_size_t_to_int_warning",
     "//build/config/compiler:wexit_time_destructors",
+    "//build/config:precompiled_headers",
     "//third_party/WebKit/public:debug_devtools",
   ]
 
   deps = [
     ":devtools_protocol_constants",
     "//base",
     "//content/public/browser",
     "//net",
   ]
 
@@ skipping 75 matching lines @@
     source = "device/webrtc/resources.grd"
     output_dir = "$root_gen_dir/chrome"
     outputs = [
       "grit/webrtc_device_provider_resources.h",
       "grit/webrtc_device_provider_resources_map.cc",
       "grit/webrtc_device_provider_resources_map.h",
       "webrtc_device_provider_resources.pak",
     ]
   }
 }