Implement support for <extensionoptions> embedding in WebUI

chrome/browser/guest_view/extension_options/extension_options_guest.cc

Index: chrome/browser/guest_view/extension_options/extension_options_guest.cc
diff --git a/chrome/browser/guest_view/extension_options/extension_options_guest.cc b/chrome/browser/guest_view/extension_options/extension_options_guest.cc
index 6d89f6fcf85c57914a6af70b78cf0fea7629ea0b..f7ca2908f72de01663b09ff9edfdecbc4ea2d6c1 100644
--- a/chrome/browser/guest_view/extension_options/extension_options_guest.cc
+++ b/chrome/browser/guest_view/extension_options/extension_options_guest.cc
@@ -64,7 +64,9 @@ void ExtensionOptionsGuest::CreateWebContents(
     return;
   }
 
-  if (extension_id != embedder_extension_id) {
+  if (extensions::Extension::IdIsValid(embedder_extension_id) &&
+      extension_id != embedder_extension_id) {
+    // Extensions cannot embed other extensions' options pages.
     callback.Run(NULL);
     return;
   }