Add ubsan bug reference to GN build.

build/config/compiler/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/android/config.gni")
 import("//build/config/chrome_build.gni")
 if (current_cpu == "arm") {
   import("//build/config/arm.gni")
 }
 if (current_cpu == "mipsel" || current_cpu == "mips64el") {
@@ skipping 66 matching lines @@
 # This is a separate config so that third_party code (which would not use the
 # source root and might have conflicting versions of some headers) can remove
 # this and specify their own include paths.
 config("default_include_dirs") {
   include_dirs = [
     "//",
     root_gen_dir,
   ]
 }
 
-# TODO(GYP): is_ubsan, is_ubsan_vptr
+# TODO(GYP) bug 527515: is_ubsan, is_ubsan_vptr
 if (!is_win) {
   using_sanitizer = is_asan || is_lsan || is_tsan || is_msan
 }
 
 # compiler ---------------------------------------------------------------------
 #
 # Base compiler configuration.
 #
 # See also "runtime_library" below for related stuff and a discussion about
 # where stuff should go. Put warning related stuff in the "warnings" config.
@@ skipping 1244 matching lines @@
       cflags += [ "-gsplit-dwarf" ]
     }
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }