Add TabContainer to Showcase

ios/showcase/suggestions/sc_suggestions_egtest.mm

 // Copyright 2016 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_matchers.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 suggestions view controller.
 @interface SCSuggestionsTestCase : ShowcaseTestCase
 @end
 
 @implementation SCSuggestionsTestCase
 
 // Tests launching ContentSuggestionsViewController.
-- (void)testLaunchAndTappingCell {
+- (void)testLaunch {
   [[EarlGrey
       selectElementWithMatcher:grey_text(@"ContentSuggestionsViewController")]
       performAction:grey_tap()];
+  [[EarlGrey selectElementWithMatcher:showcase_matchers::FirstLevelBackButton()]
+      performAction:grey_tap()];
 }
 
 @end