Add Undefined Behaviour sanitizer support to GN.

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/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/ui.gni")
@@ skipping 150 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) {
+    defines += [ "UNDEFINED_SANITIZER" ]
+  }
   if (enable_webrtc) {
     defines += [ "ENABLE_WEBRTC=1" ]
   }
   if (disable_ftp_support) {
     defines += [ "DISABLE_FTP_SUPPORT=1" ]
   }
   if (!enable_nacl) {
     defines += [ "DISABLE_NACL" ]
   }
   if (enable_extensions) {
@@ skipping 265 matching lines @@
     # This error doesn't happen every time. In VS2013, it seems if the .pch
     # 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 && !is_official_build && !use_goma) {
     precompiled_header = "build/precompile.h"
     precompiled_source = "//build/precompile.h"
   }
 }