Fix a race between navigation and an interstitial.

content/public/browser/web_contents.h

Index: content/public/browser/web_contents.h
diff --git a/content/public/browser/web_contents.h b/content/public/browser/web_contents.h
index ea487a2eb0370fb7f3177d393d28dc2cf60b1151..78cd7632e64649f004ebd5705646a7c13ca5d7b1 100644
--- a/content/public/browser/web_contents.h
+++ b/content/public/browser/web_contents.h
@@ -562,8 +562,12 @@ class WebContents : public PageNavigator,
   // Various other systems need to know about our interstitials.
   virtual bool ShowingInterstitialPage() const = 0;
 
-  // Returns the currently showing interstitial, nullptr if no interstitial is
-  // showing.
+  // Returns the currently visible interstitial, nullptr if no interstitial is
+  // visible. Note: This returns nullptr from the time the interstitial page has
+  // Show() called on it until the interstitial content is ready and the
+  // interstitial is displayed.
+  //
+  // Compare to InterstitialPage::GetInterstitialPage.
   virtual InterstitialPage* GetInterstitialPage() const = 0;
 
   // Misc state & callbacks ----------------------------------------------------