Add use_rtti gn arg to enable rtti globally in the 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")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/nacl/config.gni")
 import("//build/toolchain/cc_wrapper.gni")
 import("//build/toolchain/toolchain.gni")
@@ skipping 60 matching lines @@
   # Linux & Mac favor speed over size.
   # TODO(brettw) it's weird that Mac and desktop Linux are different. We should
   # explore favoring size over speed in this case as well.
   optimize_for_size = is_android || is_ios
 
   # Enable fatal linker warnings. Building Chromium with certain versions
   # of binutils can cause linker warning.
   # See: https://bugs.chromium.org/p/chromium/issues/detail?id=457359
   fatal_linker_warnings = true
 
+  # Build with C++ RTTI enabled. Chromium builds without RTTI by default,
+  # but some sanitizers are known to require it, like CFI diagnostics
+  # and UBsan variants.
+  use_rtti = use_cfi_diag || is_ubsan_vptr || is_ubsan_security
+
   # AFDO (Automatic Feedback Directed Optimizer) is a form of profile-guided
   # optimization that GCC supports. It used by ChromeOS in their official
   # builds. To use it, set auto_profile_path to the path to a file containing
   # the needed gcov profiling data.
   auto_profile_path = ""
 
   # Optimize for coverage guided fuzzing (balance between speed and number of
   # branches)
   optimize_for_fuzzing = false
 }
@@ skipping 1090 matching lines @@
 #
 # Allows turning Run-Time Type Identification on or off.
 
 config("rtti") {
   if (is_win) {
     cflags_cc = [ "/GR" ]
   } else {
     cflags_cc = [ "-frtti" ]
   }
 }
+
 config("no_rtti") {
-  # CFI diagnostics and UBsan vptr require RTTI.
-  if (!use_cfi_diag && !is_ubsan_vptr && !is_ubsan_security) {
+  # Some sanitizer configs may require RTTI to be left enabled globally
+  if (!use_rtti) {
     if (is_win) {
       cflags_cc = [ "/GR-" ]
     } else {
       cflags_cc = [ "-fno-rtti" ]
       cflags_objcc = cflags_cc
     }
   }
 }
 
 # Warnings ---------------------------------------------------------------------
@@ skipping 460 matching lines @@
 
 if (is_ios || is_mac) {
   # On Mac and iOS, this enables support for ARC (automatic ref-counting).
   # See http://clang.llvm.org/docs/AutomaticReferenceCounting.html.
   config("enable_arc") {
     common_flags = [ "-fobjc-arc" ]
     cflags_objc = common_flags
     cflags_objcc = common_flags
   }
 }