Fix a race between navigation and an interstitial.

content/public/browser/web_contents.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_H_
 #define CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 544 matching lines @@
   // Focuses the first (last if |reverse| is true) element in the page.
   // Invoked when this tab is getting the focus through tab traversal (|reverse|
   // is true when using Shift-Tab).
   virtual void FocusThroughTabTraversal(bool reverse) = 0;
 
   // Interstitials -------------------------------------------------------------
 
   // 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 ----------------------------------------------------
 
   // Check whether we can do the saving page operation this page given its MIME
   // type.
   virtual bool IsSavable() = 0;
 
   // Prepare for saving the current web page to disk.
   virtual void OnSavePage() = 0;
@@ skipping 254 matching lines @@
 
  private:
   // This interface should only be implemented inside content.
   friend class WebContentsImpl;
   WebContents() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_H_