Suppress some additional msvs warnings (GN).

third_party/BUILD.gn

 # Copyright 2014 PDFium 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("../pdfium.gni")
 
 group("third_party") {
   deps = [
     ":bigint",
     ":fx_freetype",
@@ skipping 234 matching lines @@
     "libjpeg/jmemsys.h",
     "libjpeg/jmorecfg.h",
     "libjpeg/jpegint.h",
     "libjpeg/jpeglib.h",
     "libjpeg/jversion.h",
     "libjpeg/makefile",
     "libjpeg/transupp.h",
   ]
 }
 
+config("fx_libopenjpeg_warnings") {
+  visibility = [ ":*" ]
+  if (is_win) {
+    cflags = [
+      # Signed/unsigned comparisons.
+      "/wd4018",
+    ]
+  }
+}
+
 source_set("fx_libopenjpeg") {
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [
     "//build/config/compiler:no_chromium_code",
     "//third_party/pdfium:pdfium_config",
+
+    # Must be after no_chromium_code for warning flags to be ordered correctly.
+    ":fx_libopenjpeg_warnings",
   ]
   sources = [
     "libopenjpeg20/bio.c",
     "libopenjpeg20/cio.c",
     "libopenjpeg20/dwt.c",
     "libopenjpeg20/event.c",
     "libopenjpeg20/function_list.c",
     "libopenjpeg20/image.c",
     "libopenjpeg20/invert.c",
     "libopenjpeg20/j2k.c",
@@ skipping 141 matching lines @@
   sources = [
     "base/logging.h",
     "base/macros.h",
     "base/numerics/safe_conversions.h",
     "base/numerics/safe_conversions_impl.h",
     "base/numerics/safe_math.h",
     "base/numerics/safe_math_impl.h",
     "base/stl_util.h",
   ]
 }