win: build fixes

services/http_server/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.
 
 shared_library("http_server") {
   sources = [
     "http_request_parser.cc",
     "http_request_parser.h",
     "http_server.cc",
   ]
 
   deps = [
     "//base",
     "//mojo/common",
     "//mojo/public/c/system:for_shared_library",
     "//mojo/public/cpp/application:standalone",
     "//mojo/public/cpp/bindings",
     "//mojo/public/cpp/utility",
     "//mojo/services/public/interfaces/network",
     "//services/http_server/public",
     "//third_party/re2",
   ]
+
+  if (is_win) {
+    cflags = [
+      # size_t to int.
+      "/wd4267",
+    ]
+  }
 }