Avoid use-after-free when InterstitialPageImpl is being torn down.

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 465086c739b551fb249e520f33be7a3aceb68384..a4f6382192466d71d0d62e94dbe230cf28129c99 100644
--- a/content/browser/frame_host/interstitial_page_impl.cc
+++ b/content/browser/frame_host/interstitial_page_impl.cc
@@ -807,6 +807,10 @@ FrameTree* InterstitialPageImpl::GetFrameTree() {
 
 void InterstitialPageImpl::Disable() {
   enabled_ = false;
+
+  // Also let the InterstitialPageNavigatorImpl know.
+  static_cast<InterstitialPageNavigatorImpl*>(frame_tree_->root()->navigator())
+      ->Disable();
 }
 
 void InterstitialPageImpl::Shutdown() {