Add the ability to unload the HistoryBackend....

chrome/test/testing_profile.h

Index: chrome/test/testing_profile.h
===================================================================
--- chrome/test/testing_profile.h	(revision 28361)
+++ chrome/test/testing_profile.h	(working copy)
@@ -89,6 +89,9 @@
   virtual HistoryService* GetHistoryService(ServiceAccessType access) {
     return history_service_.get();
   }
+  virtual HistoryService* GetHistoryServiceWithoutCreating() {
+    return history_service_.get();
+  }
   void set_has_history_service(bool has_history_service) {
     has_history_service_ = has_history_service;
   }