Disable flaky showcase tests

ios/showcase/tab/sc_tab_egtest.mm

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import <EarlGrey/EarlGrey.h>
 
 #import "ios/showcase/test/showcase_eg_utils.h"
 #import "ios/showcase/test/showcase_test_case.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 // Tests for the tab container view controller.
 @interface SCTabTestCase : ShowcaseTestCase
 @end
 
 @implementation SCTabTestCase
 
 // Tests launching TopToolbarTabViewController.
-- (void)testLaunchWithTopToolbar {
+// TODO(crbug.com/710662): re-enable this test.
+- (void)FLAKY_testLaunchWithTopToolbar {
   showcase_utils::Open(@"TopToolbarTabViewController");
   showcase_utils::Close();
 }
 
 // Tests launching BottomToolbarTabViewController.
-- (void)testLaunchWithBottomToolbar {
+// TODO(crbug.com/710662): re-enable this test.
+- (void)FLAKY_testLaunchWithBottomToolbar {
   showcase_utils::Open(@"BottomToolbarTabViewController");
   showcase_utils::Close();
 }
 
 @end