Add GN configs for -fsanitizer=null.

build/config/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.
 
 import("//build/config/allocator.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/crypto.gni")
 import("//build/config/dcheck_always_on.gni")
 import("//build/config/features.gni")
@@ skipping 147 matching lines @@
   if (is_tsan) {
     defines += [
       "THREAD_SANITIZER",
       "DYNAMIC_ANNOTATIONS_EXTERNAL_IMPL=1",
       "WTF_USE_DYNAMIC_ANNOTATIONS_NOIMPL=1",
     ]
   }
   if (is_msan) {
     defines += [ "MEMORY_SANITIZER" ]
   }
-  if (is_ubsan || is_ubsan_vptr || is_ubsan_security) {
+  if (is_ubsan || is_ubsan_null || is_ubsan_vptr || is_ubsan_security) {
     defines += [ "UNDEFINED_SANITIZER" ]
   }
   if (enable_webrtc) {
     defines += [ "ENABLE_WEBRTC=1" ]
   }
   if (!enable_nacl) {
     defines += [ "DISABLE_NACL" ]
   }
   if (enable_extensions) {
     defines += [ "ENABLE_EXTENSIONS=1" ]
@@ skipping 268 matching lines @@
       # file doesn't exist, no error will be generated (probably MS tested this
       # case but forgot the other one?). To reproduce this error, do a build,
       # then delete the precompile.c.obj file, then build again.
       cflags_c = [ "/wd4206" ]
     } else if (is_mac) {
       precompiled_header = "build/precompile.h"
       precompiled_source = "//build/precompile.h"
     }
   }
 }