Disable ProxyAuthDialogOnUserBoardScreen

It is flaky. Error:

[FATAL:profile_destroyer.cc(56)] Check failed: hosts.empty() ||
profile->IsOffTheRecord() ||
content::RenderProcessHost::run_renderer_in_process().
Profile still has 1 hosts

0x7f035e2968ec base::debug::StackTrace::StackTrace()
0x7f035e2bc41c logging::LogMessage::~LogMessage()
0x0000025be6d8 ProfileDestroyer::DestroyProfileWhenAppropriate()
0x0000023da2a0 std::__1::__tree<>::destroy()
0x0000023da1e9 ProfileManager::~ProfileManager()
0x0000023d1ace ProfileManager::~ProfileManager()
0x000002559112 BrowserProcessImpl::StartTearDown()
0x0000022ad6f2 ChromeBrowserMainParts::PostMainMessageLoopRun()
0x000001e0a813 chromeos::ChromeBrowserMainPartsChromeos::PostMainMessageLoopRun()
0x7f035a63837a content::BrowserMainLoop::ShutdownThreadsAndCleanUp()
...

Bug=772072

Bug: 
Change-Id: I91391979088148a9857728f5c7b30d397b8335f2
Reviewed-on: https://chromium-review.googlesource.com/703034Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Ehsan Chiniforooshan <chiniforooshan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#506834}

chrome/browser/chromeos/login/proxy_auth_dialog_browsertest.cc

@@ -90,15 +90,9 @@ IN_PROC_BROWSER_TEST_F(ProxyAuthOnUserBoardScreenTest,
   StartupUtils::MarkOobeCompleted();
 }
 
-// Times out under MSan, and is flaky for ASan: https://crbug.com/481651
-#if defined(MEMORY_SANITIZER) || defined(ADDRESS_SANITIZER)
-#define MAYBE_ProxyAuthDialogOnUserBoardScreen \
-  DISABLED_ProxyAuthDialogOnUserBoardScreen
-#else
-#define MAYBE_ProxyAuthDialogOnUserBoardScreen ProxyAuthDialogOnUserBoardScreen
-#endif
+// Flaky: https://crbug.com/481651 and https://crbug.com/772072
 IN_PROC_BROWSER_TEST_F(ProxyAuthOnUserBoardScreenTest,
-                       MAYBE_ProxyAuthDialogOnUserBoardScreen) {
+                       DISABLED_ProxyAuthDialogOnUserBoardScreen) {
   LoginDisplayHost* login_display_host = LoginDisplayHost::default_host();
   WebUILoginView* web_ui_login_view = login_display_host->GetWebUILoginView();
   OobeUI* oobe_ui = web_ui_login_view->GetOobeUI();