Fix a race between navigation and an interstitial.

content/browser/frame_host/navigation_controller_impl.cc

Index: content/browser/frame_host/navigation_controller_impl.cc
diff --git a/content/browser/frame_host/navigation_controller_impl.cc b/content/browser/frame_host/navigation_controller_impl.cc
index 1f07ec664e0b2f0f212e746e2fb5d89d9d80db42..90d3a376f7f41b52d07e6fbe99473e575a380802 100644
--- a/content/browser/frame_host/navigation_controller_impl.cc
+++ b/content/browser/frame_host/navigation_controller_impl.cc
@@ -1882,8 +1882,10 @@ void NavigationControllerImpl::NavigateToPendingEntry(ReloadType reload_type) {
 
     // If an interstitial page is showing, we want to close it to get back

[Charlie Reis, 2017/06/21 06:02:31]

"is showing or is about to show"?
(It's worth clarifying why we're using this one instead of
delegate_->GetInterstitialPage() if we can't replace all the uses.)

     // to what was showing before.
-    if (delegate_->GetInterstitialPage())
-      delegate_->GetInterstitialPage()->DontProceed();
+    InterstitialPage* interstitial =
+        InterstitialPage::GetInterstitialPage(GetWebContents());
+    if (interstitial)
+      interstitial->DontProceed();
 
     DiscardNonCommittedEntries();
     return;