Fix another source of flakiness in ErrorPageTest

chrome/test/automation/tab_proxy.h

 // Copyright (c) 2006-2008 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.
 
 #ifndef CHROME_TEST_AUTOMATION_TAB_PROXY_H_
 #define CHROME_TEST_AUTOMATION_TAB_PROXY_H_
 
 #include "build/build_config.h"
 
 #if defined(OS_WIN)
@@ skipping 102 matching lines @@
   // Replaces a vector contents with the redirect chain out of the given URL.
   // Returns true on success. Failure may be due to being unable to send the
   // message, parse the response, or a failure of the history system in the
   // browser.
   bool GetRedirectsFrom(const GURL& source_url, std::vector<GURL>* redirects);
 
   // Equivalent to hitting the Back button. This is a synchronous call and
   // hence blocks until the navigation completes.
   AutomationMsg_NavigationResponseValues GoBack();
 
+  // Equivalent to hitting the Back button. This is a synchronous call and
+  // hence blocks until the |number_of_navigations| navigations complete.
+  AutomationMsg_NavigationResponseValues GoBackBlockUntilNavigationsComplete(
+      int number_of_navigations);
+
   // Equivalent to hitting the Forward button. This is a synchronous call and
   // hence blocks until the navigation completes.
   AutomationMsg_NavigationResponseValues GoForward();
 
+  // Equivalent to hitting the Forward button. This is a synchronous call and
+  // hence blocks until the |number_of_navigations| navigations complete.
+  AutomationMsg_NavigationResponseValues GoForwardBlockUntilNavigationsComplete(
+      int number_of_navigations);
+
   // Equivalent to hitting the Reload button. This is a synchronous call and
   // hence blocks until the navigation completes.
   AutomationMsg_NavigationResponseValues Reload();
 
   // Closes the tab. This is synchronous, but does NOT block until the tab has
   // closed, rather it blocks until the browser has initiated the close. Use
   // Close(true) if you need to block until tab completely closes.
   //
   // Note that this proxy is invalid after this call.
   bool Close();
@@ skipping 193 matching lines @@
   void OnMessageReceived(const IPC::Message& message);
  protected:
   virtual ~TabProxy() {}
  private:
   Lock list_lock_;  // Protects the observers_list_.
   ObserverList<TabProxyDelegate> observers_list_;
   DISALLOW_COPY_AND_ASSIGN(TabProxy);
 };
 
 #endif  // CHROME_TEST_AUTOMATION_TAB_PROXY_H_