Don't show current RenderWidgetHostView while interstitial is showing.

content/browser/frame_host/interstitial_page_impl.cc

Index: content/browser/frame_host/interstitial_page_impl.cc
diff --git a/content/browser/frame_host/interstitial_page_impl.cc b/content/browser/frame_host/interstitial_page_impl.cc
index 90e4de3815895910f0db1c9d41d0b4cf0672f708..60dce63f16d340a4aee2ea5694a75829685f0ce7 100644
--- a/content/browser/frame_host/interstitial_page_impl.cc
+++ b/content/browser/frame_host/interstitial_page_impl.cc
@@ -544,6 +544,11 @@ const std::string& InterstitialPageImpl::GetUserAgentOverride() const {
   return base::EmptyString();
 }
 
+bool InterstitialPageImpl::ShowingInterstitialPage() const {
+  // An interstitial page never shows a second interstitial.
+  return false;
+}
+
 RendererPreferences InterstitialPageImpl::GetRendererPrefs(
     BrowserContext* browser_context) const {
   delegate_->OverrideRendererPrefs(&renderer_preferences_);