Minor fixes for the GN Windows build.

components/pdf/renderer/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/features.gni")
 
 static_library("renderer") {
   sources = [
     "pepper_pdf_host.cc",
     "pepper_pdf_host.h",
     "pdf_resource_util.cc",
     "pdf_resource_util.h",
     "ppb_pdf_impl.cc",
     "ppb_pdf_impl.h",
   ]
 
   deps = [
     "//base",
     "//components/pdf/common",
     "//components/resources:components_resources",
     "//components/strings",
     "//content/public/renderer",
     "//ppapi:ppapi_shared",
     "//third_party/icu",
     "//v8",
     "//third_party/WebKit/public:blink_minimal",
   ]
 
   if (is_win) {
-    cflags += [
+    cflags = [
       "/wd4267"  # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     ]
   }
 }