Add precompiled headers to GN build for large targets.

ppapi/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.
 
 copy("copy_test_files") {
   visibility = [ ":*" ]
   sources = [
     # Keep "test_case.html.mock-http-headers" with "test_case.html".
     "tests/ppapi_nacl_tests_newlib.nmf",
     "tests/test_case.html",
@@ skipping 16 matching lines @@
   ]
 }
 
 import("//ppapi/ppapi_sources.gni")
 import("//testing/test.gni")
 
 shared_library("ppapi_tests") {
   sources = ppapi_sources.test_common_source_files +
             ppapi_sources.test_trusted_source_files
 
+  configs += [ "//build/config:precompiled_headers" ]
   defines = [ "GL_GLEXT_PROTOTYPES" ]
   include_dirs = [ "lib/gl/include" ]
 
   deps = [
     "//ppapi/cpp",
     "//ppapi/shared_impl",
     ":copy_test_files",
     ":copy_test_files2",
   ]
 }
@@ skipping 84 matching lines @@
 
 executable("pepper_hash_for_uma") {
   sources = [
     "tools/pepper_hash_for_uma.cc",
   ]
 
   deps = [
     "//base",
   ]
 }