Try again to fix bug 20968, this time not breaking browser

chrome/browser/extensions/extension_browsertests_misc.cc

 // Copyright (c) 2009 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.
 
 #include "base/ref_counted.h"
 #include "chrome/browser/browser.h"
 #include "chrome/browser/browser_list.h"
 #include "chrome/browser/renderer_host/render_view_host.h"
 #include "chrome/browser/extensions/extension_browsertest.h"
 #include "chrome/browser/extensions/extension_host.h"
@@ skipping 220 matching lines @@
                       .AppendASCII("samples")
                       .AppendASCII("subscribe_page_action")
                       .AppendASCII("subscribe.html");
   subscribe = subscribe.StripTrailingSeparators();
 
   FilePath feed_dir = test_dir.AppendASCII("feeds")
                               .AppendASCII(feed_page.c_str());
 
   return GURL(net::FilePathToFileURL(subscribe).spec() +
               std::string("?") +
-              net::FilePathToFileURL(feed_dir).spec());
+              net::FilePathToFileURL(feed_dir).spec() +
+              "&synchronous");  // synchronous XHR for easier testing.
 }
 
 static const wchar_t* jscript_feed_title =
     L"window.domAutomationController.send("
     L"  document.getElementById('title') ? "
     L"    document.getElementById('title').textContent : "
     L"    \"element 'title' not found\""
     L");";
 static const wchar_t* jscript_anchor =
     L"window.domAutomationController.send("
@@ skipping 315 matching lines @@
       browser(),
       GURL("about:blank"),
       "chrome-extension://aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa/newtab.html");
 
   // Extension API should fail.
   bool result = false;
   ui_test_utils::ExecuteJavaScriptAndExtractBool(
       newtab->render_view_host(), L"", L"testExtensionApi()", &result);
   EXPECT_FALSE(result);
 }