Disable ProfileListDesktopBrowserTest.SignOut on Linux

chrome/browser/profiles/profile_list_desktop_browsertest.cc

Index: chrome/browser/profiles/profile_list_desktop_browsertest.cc
diff --git a/chrome/browser/profiles/profile_list_desktop_browsertest.cc b/chrome/browser/profiles/profile_list_desktop_browsertest.cc
index 2a189253117b5bbbbb049022d4f4c62288c082f7..b4db78abe15b875172fb8f72867e3cc7703f4bbd 100644
--- a/chrome/browser/profiles/profile_list_desktop_browsertest.cc
+++ b/chrome/browser/profiles/profile_list_desktop_browsertest.cc
@@ -59,6 +59,9 @@ class ProfileListDesktopBrowserTest : public InProcessBrowserTest {
 // This test doesn't make sense for Chrome OS since it has a different
 // multi-profiles menu in the system tray instead.
 #define MAYBE_SignOut DISABLED_SignOut
+#elif defined(OS_LINUX)
+// Flaky on Linux debug builds with libc++ (https://crbug.com/734875)
+#define MAYBE_SignOut DISABLED_SignOut
 #else
 #define MAYBE_SignOut SignOut
 #endif