Disabling PasswordsSettingsTestCase/testEditUsernameFails for device iOS

The test fails iPad 6th on iOS 12.4.

Bug: 1140400
Change-Id: Ic4016aee1ad1444af112a4c1ceb34e7829533758
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2485934
Commit-Queue: Jérôme Lebel <jlebel@chromium.org>
Auto-Submit: Jérôme Lebel <jlebel@chromium.org>
Reviewed-by: Viktor Semeniuk <vsemeniuk@google.com>
Cr-Commit-Position: refs/heads/master@{#818868}

ios/chrome/browser/ui/settings/password/passwords_settings_egtest.mm

@@ -1484,7 +1484,13 @@ void CopyPasswordDetailWithID(int detail_id) {
 
 // Checks that attempts to edit a username to a value which is already used for
 // the same domain fails.
-- (void)testEditUsernameFails {
+// TODO(crbug.com/1140400): Fails on device for iPad 6th iOS 12.4.
+#if TARGET_IPHONE_SIMULATOR
+#define MAYBE_testEditUsernameFails testEditUsernameFails
+#else
+#define MAYBE_testEditUsernameFails DISABLED_testEditUsernameFails
+#endif
+- (void)MAYBE_testEditUsernameFails {
   GREYAssert(
       [PasswordSettingsAppInterface saveExamplePassword:@"concrete password"
                                                userName:@"concrete username1"