[Chromedriver] Allow access to chrome extension within iframe.

chrome/test/chromedriver/chrome_launcher.cc

 // Copyright (c) 2013 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 "chrome/test/chromedriver/chrome_launcher.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 66 matching lines @@
     "disable-background-networking",
     "disable-web-resources",
     "safebrowsing-disable-auto-update",
     "disable-client-side-phishing-detection",
     "disable-default-apps",
     "enable-logging",
     "log-level=0",
     "password-store=basic",
     "use-mock-keychain",
     "test-type=webdriver",
+    "force-fieldtrials=SiteIsolationExtensions/Control",
 };
 
 const char* const kAndroidSwitches[] = {
     "disable-fre", "enable-remote-debugging",
 };
 
 #if defined(OS_LINUX)
 const char kEnableCrashReport[] = "enable-crash-reporter-for-testing";
 #endif
 
@@ skipping 779 matching lines @@
   // Write empty "First Run" file, otherwise Chrome will wipe the default
   // profile that was written.
   if (base::WriteFile(
           user_data_dir.Append(chrome::kFirstRunSentinel), "", 0) != 0) {
     return Status(kUnknownError, "failed to write first run file");
   }
   return Status(kOk);
 }
 
 }  // namespace internal