Add UBsan vtpr support to GN.

build/config/sanitizers/BUILD.gn

Index: build/config/sanitizers/BUILD.gn
diff --git a/build/config/sanitizers/BUILD.gn b/build/config/sanitizers/BUILD.gn
index 4394014616cd5e22a45d7ef91ecf968e7f535eee..0a037e1dfe4e78e37bf576ca6888b7d6aa635cf4 100644
--- a/build/config/sanitizers/BUILD.gn
+++ b/build/config/sanitizers/BUILD.gn
@@ -13,7 +13,7 @@ group("deps") {
     use_custom_libcxx = true
   }
 
-  if (is_asan || is_lsan || is_tsan || is_msan || is_ubsan) {
+  if (using_sanitizer) {
     public_configs = [ ":sanitizer_options_link_helper" ]
     deps = [
       ":options_sources",
@@ -45,6 +45,9 @@ config("sanitizer_options_link_helper") {
   if (is_ubsan) {
     ldflags += [ "-fsanitize=undefined" ]
   }
+  if (is_ubsan_vptr) {
+    ldflags += [ "-fsanitize=vptr" ]
+  }
 }
 
 source_set("options_sources") {
@@ -158,6 +161,14 @@ config("default_sanitizer_flags") {
         "-pbqp-coalescing",
       ]
     }
+    if (is_ubsan_vptr) {
+      ubsan_vptr_blacklist_path =
+          rebase_path("//tools/ubsan/vptr_blacklist.txt", root_build_dir)
+      cflags += [
+        "-fsanitize=vptr",
+        "-fsanitize-blacklist=$ubsan_vptr_blacklist_path",
+      ]
+    }
     if (is_cfi && !is_nacl) {
       cfi_blacklist_path =
           rebase_path("//tools/cfi/blacklist.txt", root_build_dir)