Disable testRegularPlusIncognito to address test flakiness.

As described in more detail here (crbug.com/1096582), this test seems to
cause testSingleSyncSignout and testSingleDisableSync to be flaky.

Added a bug to re-enable testRegularPlusIncognito.

Bug: 1094932

Change-Id: I87ce718f3d533f5684d97ff5aadb6f8cf8c9ba2f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2252638Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Commit-Queue: Caitlin Fischer <caitlinfischer@google.com>
Cr-Commit-Position: refs/heads/master@{#780255}

ios/chrome/browser/metrics/ukm_egtest.mm

@@ -155,13 +155,8 @@ using chrome_test_util::SettingsDoneButton;
 //
 // Corresponds to RegularPlusIncognitoCheck in //chrome/browser/metrics/
 // ukm_browsertest.cc.
-#if defined(CHROME_EARL_GREY_1)
-// TODO(crbug.com/1033726): EG1 Test fails on iOS 12.
-#define MAYBE_testRegularPlusIncognito DISABLED_testRegularPlusIncognito
-#else
-#define MAYBE_testRegularPlusIncognito testRegularPlusIncognito
-#endif
-- (void)MAYBE_testRegularPlusIncognito {
+// TODO(crbug.com/1096582) Re-enable the test.
+- (void)DISABLED_testRegularPlusIncognito {
   const uint64_t originalClientID = [MetricsAppInterface UKMClientID];
 
   [self openNewIncognitoTab];