Use the old back button on Terms of Service.

ios/chrome/browser/ui/first_run/first_run_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 <XCTest/XCTest.h>
 
 #include "base/strings/sys_string_conversions.h"
 #include "components/metrics/metrics_pref_names.h"
 #include "components/metrics/metrics_reporting_default_state.h"
@@ skipping 101 matching lines @@
 
   id<GREYMatcher> termsOfServiceLink =
       grey_accessibilityLabel(@"Terms of Service");
   [[EarlGrey selectElementWithMatcher:termsOfServiceLink]
       performAction:grey_tap()];
 
   [[EarlGrey selectElementWithMatcher:grey_text(l10n_util::GetNSString(
                                           IDS_IOS_FIRSTRUN_TERMS_TITLE))]
       assertWithMatcher:grey_sufficientlyVisible()];
 
-  [[EarlGrey selectElementWithMatcher:grey_accessibilityID(@"back_bar_button")]
+  [[EarlGrey selectElementWithMatcher:grey_accessibilityID(@"ic_arrow_back")]
       performAction:grey_tap()];
 
   // Ensure we went back to the First Run screen.
   [[EarlGrey selectElementWithMatcher:termsOfServiceLink]
       assertWithMatcher:grey_sufficientlyVisible()];
 }
 
 // Toggle the UMA checkbox.
 - (void)testToggleMetricsOn {
   [chrome_test_util::GetMainController() showFirstRunUI];
@@ skipping 86 matching lines @@
                   @"Sync shouldn't have finished its original setup yet");
 
   // Close Settings, user is still signed in and sync is now starting.
   TapButtonWithLabelId(IDS_IOS_NAVIGATION_BAR_DONE_BUTTON);
   AssertAuthenticatedIdentityInActiveProfile(identity);
   GREYAssertTrue(sync_service->HasFinishedInitialSetup(),
                  @"Sync should have finished its original setup");
 }
 
 @end