Check for registry and extension existence before web_accessible_resources.

extensions/browser/extension_navigation_throttle.cc

 // Copyright 2016 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.
 
 #include "extensions/browser/extension_navigation_throttle.h"
 
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/navigation_handle.h"
 #include "content/public/browser/render_frame_host.h"
 #include "content/public/browser/web_contents.h"
@@ skipping 60 matching lines @@
   }
 
   if (!external_ancestor)
     return content::NavigationThrottle::PROCEED;
 
   // Since there was at least one origin different than the navigation URL,
   // explicitly check for the resource in web_accessible_resources.
   std::string resource_path = navigation_handle()->GetURL().path();
   ExtensionRegistry* registry = ExtensionRegistry::Get(
       navigation_handle()->GetWebContents()->GetBrowserContext());
+  if (!registry)
+    return content::NavigationThrottle::BLOCK_REQUEST;

[asargent_no_longer_on_chrome, 2016/06/08 18:30:13]

Off the top of my head I can't think of situations where ExtensionRegistry::Get
would return null here - we use the same object for regular and incognito
profiles because of
https://cs.chromium.org/chromium/src/extensions/browser/extension_registry_fa...

Maybe a race condition at shutdown or something?

Anyhow, it problem doesn't hurt to have the check here. 

+
   const extensions::Extension* extension =
       registry->enabled_extensions().GetByID(
           navigation_handle()->GetURL().host());
+  if (!extension)
+    return content::NavigationThrottle::BLOCK_REQUEST;
 
   if (WebAccessibleResourcesInfo::IsResourceWebAccessible(extension,
                                                           resource_path)) {
     return content::NavigationThrottle::PROCEED;
   }
 
   return content::NavigationThrottle::BLOCK_REQUEST;
 }
 
 }  // namespace extensions