Convert the re2 GYP targets to be generated by GN.

third_party/re2/BUILD.gn

 # Copyright (c) 2013 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.
 
+gyp_file = "//out/gn_gyp/third_party/re2/re2.gyp"
+
 config("re2_config") {
   include_dirs = [ "." ]
 }
 
-gyp_file = "re2.gyp"
-external = true
-
 static_library("re2") {
   sources = [
     "mswin/stdint.h",
     "re2/bitstate.cc",
     "re2/compile.cc",
     "re2/dfa.cc",
     "re2/filtered_re2.cc",
     "re2/filtered_re2.h",
     "re2/mimics_pcre.cc",
     "re2/nfa.cc",
@@ skipping 41 matching lines @@
   configs -= "//build/config/compiler:chromium_code"
   configs += "//build/config/compiler:no_chromium_code"
   direct_dependent_configs = [ ":re2_config" ]
 
   deps = [
     "//base/third_party/dynamic_annotations",
   ]
 
   if (is_win) {
     include_dirs = [ "mswin" ]
-    # TODO(brettw) 'msvs_disabled_warnings': [ 4018, 4722, 4267 ],
   } else {
     sources -= "mswin/stdint.h"
   }
 }