Support interstitials with no primary button

components/security_interstitials/content/security_interstitial_controller_client.cc

Index: components/security_interstitials/content/security_interstitial_controller_client.cc
diff --git a/components/security_interstitials/content/security_interstitial_controller_client.cc b/components/security_interstitials/content/security_interstitial_controller_client.cc
index 150505e5f5ad71b93849ad88951833276703d720..a40f0d438192e84360f65a21659fefd6d01613ed 100644
--- a/components/security_interstitials/content/security_interstitial_controller_client.cc
+++ b/components/security_interstitials/content/security_interstitial_controller_client.cc
@@ -46,6 +46,10 @@ void SecurityInterstitialControllerClient::GoBack() {
   interstitial_page_->DontProceed();
 }
 
+bool SecurityInterstitialControllerClient::CanGoBack() {
+  return web_contents_->GetController().CanGoBack();
+}
+
 void SecurityInterstitialControllerClient::GoBackAfterNavigationCommitted() {
   // 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