Support interstitials with no primary button

ios/chrome/browser/interstitials/ios_chrome_controller_client.h

 // Copyright 2015 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.
 
 #ifndef IOS_CHROME_BROWSER_INTERSTITIALS_IOS_CHROME_CONTROLLER_CLIENT_H_
 #define IOS_CHROME_BROWSER_INTERSTITIALS_IOS_CHROME_CONTROLLER_CLIENT_H_
 
 #include <string>
 
 #include "base/macros.h"
@@ skipping 19 matching lines @@
       std::unique_ptr<security_interstitials::MetricsHelper> metrics_helper);
   ~IOSChromeControllerClient() override;
 
   void SetWebInterstitial(web::WebInterstitial* web_interstitial);
 
  private:
   // security_interstitials::ControllerClient implementation.
   bool CanLaunchDateAndTimeSettings() override;
   void LaunchDateAndTimeSettings() override;
   void GoBack() override;
+  bool CanGoBack() override;
   void GoBackAfterNavigationCommitted() override;
   void Proceed() override;
   void Reload() override;
   void OpenUrlInCurrentTab(const GURL& url) override;
   const std::string& GetApplicationLocale() const override;
   PrefService* GetPrefService() override;
   const std::string GetExtendedReportingPrefName() const override;
 
   web::WebState* web_state_;
   web::WebInterstitial* web_interstitial_;
 
   DISALLOW_COPY_AND_ASSIGN(IOSChromeControllerClient);
 };
 
 #endif  // IOS_CHROME_BROWSER_INTERSTITIALS_IOS_CHROME_CONTROLLER_CLIENT_H_