Add UBsan vtpr support to GN.

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")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/nacl/config.gni")
 import("//build/toolchain/ccache.gni")
 
@@ skipping 830 matching lines @@
 # rtti ------------------------------------------------------------------------
 #
 # Allows turning Run-Time Type Identification on or off.
 
 config("rtti") {
   if (is_win) {
     cflags_cc = [ "/GR" ]
   }
 }
 config("no_rtti") {
-  # CFI diagnostics require RTTI.
-  if (!use_cfi_diag) {
+  # CFI diagnostics and UBsan vptr require RTTI.
+  if (!use_cfi_diag && !is_ubsan_vptr) {
     if (is_win) {
       cflags_cc = [ "/GR-" ]
     } else {
       cflags_cc = [ "-fno-rtti" ]
       cflags_objcc = cflags_cc
     }
   }
 }
 
 # Warnings ---------------------------------------------------------------------
@@ skipping 305 matching lines @@
   if (symbol_level == 0) {
     configs = [ ":no_symbols" ]
   } else if (symbol_level == 1) {
     configs = [ ":minimal_symbols" ]
   } else if (symbol_level == 2) {
     configs = [ ":symbols" ]
   } else {
     assert(false)
   }
 }