Disable ResetMediaFeed_WebContentsDestroyed under UBSan

The UBSan VPtr configuration fairly reliably repros the issue in
https://crbug.com/1124983. However, this is (probably) the last issue
blocking promoting the UBSan VPtr configuration from being promoted into
the main waterfall, so disable the test under UBSan for now.

Bug: 1124983, 1137496
Change-Id: Ie0c72c7e41c285f28787db05aefac3a99c73080f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2589038
Commit-Queue: Arthur Eubanks <aeubanks@google.com>
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837814}

chrome/browser/media/feeds/media_feeds_browsertest.cc

@@ -925,7 +925,8 @@ IN_PROC_BROWSER_TEST_F(MediaFeedsBrowserTest,
 }
 
 // Flaky on lacros and windows: crbug.com/1124983
-#if BUILDFLAG(IS_CHROMEOS_LACROS) || defined(OS_WIN)
+#if BUILDFLAG(IS_CHROMEOS_LACROS) || defined(OS_WIN) || \
+    defined(UNDEFINED_SANITIZER)
 #define MAYBE_ResetMediaFeed_WebContentsDestroyed \
   DISABLED_ResetMediaFeed_WebContentsDestroyed
 #else