Check for registry and extension existence before web_accessible_resources.

extensions/browser/extension_navigation_throttle.cc

Index: extensions/browser/extension_navigation_throttle.cc
diff --git a/extensions/browser/extension_navigation_throttle.cc b/extensions/browser/extension_navigation_throttle.cc
index 3c63dd76bf152bc75bef182b82b3a6b1fd2b09ca..235c779cafb7aa859eef19f844940fe92ac57c7d 100644
--- a/extensions/browser/extension_navigation_throttle.cc
+++ b/extensions/browser/extension_navigation_throttle.cc
@@ -78,9 +78,14 @@ ExtensionNavigationThrottle::WillStartRequest() {
   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)) {