Disable NtpExtensionBubbleViewBrowserTest.TestBubbleClosedAfterExtensionUninstall on linux

It is flaky on Linux Tests (dbg). E.g.
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Linux%20Tests%20%28dbg%29%281%29%2832%29/51783

Bug: 851655
No-try: True
No-presubmit: True
Change-Id: I1413c50f37054dc073afc0b6aa2fb281c11ca2ac
Reviewed-on: https://chromium-review.googlesource.com/1160502Reviewed-by: Christos Froussios <cfroussios@chromium.org>
Commit-Queue: Christos Froussios <cfroussios@chromium.org>
Cr-Commit-Position: refs/heads/master@{#580136}

chrome/browser/ui/views/extensions/extension_message_bubble_view_browsertest.cc

@@ -273,7 +273,7 @@ IN_PROC_BROWSER_TEST_F(NtpExtensionBubbleViewBrowserTest,
 }
 
 // Flaky on Mac https://crbug.com/851655
-#if defined(OS_MACOSX)
+#if defined(OS_MACOSX) || defined(OS_LINUX)
 #define MAYBE_TestBubbleClosedAfterExtensionUninstall \
   DISABLED_TestBubbleClosedAfterExtensionUninstall
 #else