Add mb_config for the new ubsan try bot.

tools/mb/mb_config.pyl

Index: tools/mb/mb_config.pyl
diff --git a/tools/mb/mb_config.pyl b/tools/mb/mb_config.pyl
index 330faf0236e152a734a4e193c02095a1ba0d85d9..25412fd2474b1a5ec491147474cfc3c52d47ff68 100644
--- a/tools/mb/mb_config.pyl
+++ b/tools/mb/mb_config.pyl
@@ -539,6 +539,7 @@
 
       'linux_chromium_rel_ng': 'gpu_tests_release_trybot',
       'linux_chromium_tsan_rel_ng': 'tsan_disable_nacl_release_trybot',
+      'linux_chromium_ubsan_rel_ng': 'ubsan_vptr_release_trybot',
 
       # This is 'release_bot' rather than 'release_trybot' because
       # 'release_trybot' includes 'dcheck_always_on', which might cause
@@ -1433,6 +1434,10 @@
       'ubsan_vptr', 'ubsan_no_recover_hack', 'release_bot',
     ],
 
+    'ubsan_vptr_release_trybot': [
+      'ubsan_vptr', 'ubsan_no_recover_hack', 'release_trybot',
+    ],
+
     'win_clang_debug_bot': [
       'clang', 'debug_bot', 'minimal_symbols',
     ],