Allow extension APIs to be called from WebUI.

chrome/browser/extensions/extension_test_message_listener.h

Index: chrome/browser/extensions/extension_test_message_listener.h
diff --git a/chrome/browser/extensions/extension_test_message_listener.h b/chrome/browser/extensions/extension_test_message_listener.h
index 7da133e36ddc0a2f89d9385ceca9241a0c23279d..557ce6ce853f67a661dfd4817eda1e449a696af4 100644
--- a/chrome/browser/extensions/extension_test_message_listener.h
+++ b/chrome/browser/extensions/extension_test_message_listener.h
@@ -106,6 +106,8 @@ class ExtensionTestMessageListener : public content::NotificationObserver {
   // Convenience method that formats int as a string and sends it.
   void Reply(int message);
 
+  void ReplyWithError(const std::string& error);
+
   // Reset the listener to listen again. No settings (such as messages to
   // listen for) are modified.
   void Reset();