Support interstitials with no primary button

components/security_interstitials/core/controller_client.h

Index: components/security_interstitials/core/controller_client.h
diff --git a/components/security_interstitials/core/controller_client.h b/components/security_interstitials/core/controller_client.h
index 33d9cece49438ed842586b792cf8a538509ad5f8..613c6bc9f7f6c53cf0c9911e66ae3f6ae4df361f 100644
--- a/components/security_interstitials/core/controller_client.h
+++ b/components/security_interstitials/core/controller_client.h
@@ -71,6 +71,8 @@ class ControllerClient {
   // Close the error and go back to the previous page. This applies to
   // situations where navigation is blocked before committing.
   virtual void GoBack() = 0;
+  // Whether it is possible to go 'Back to safety'.
+  virtual bool CanGoBack() = 0;
 
   // If the offending entry has committed, go back or to a safe page without
   // closing the error page. This error page will be closed when the new page