Make tab_capture_end2end_tests work as a regular windowed_test_launcher.

testing/xvfb.py

 #!/usr/bin/env python
 # Copyright (c) 2012 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.
 
 """Runs tests with Xvfb and Openbox on Linux and normally on other platforms."""
 
 import os
 import os.path
 import platform
@@ skipping 30 matching lines @@
   thread.join(timeout_in_seconds)
   if thread.is_alive():
     print >> sys.stderr, 'Xvfb running after SIGTERM and SIGKILL; good luck!'
 
 
 def run_executable(cmd, env):
   """Runs an executable within Xvfb on Linux or normally on other platforms.
 
   Returns the exit code of the specified commandline, or 1 on failure.
   """
-  if sys.platform == 'linux2':
+
+  # It might seem counterintuitive to support a --no-xvfb flag in a script
+  # whose only job is to start xvfb, but doing so allows us to consolidate
+  # the logic in the layers of buildbot scripts so that we *always* use
+  # xvfb by default and don't have to worry about the distinction, it
+  # can remain solely under the control of the test invocation itself.
+  use_xvfb = True
+  if '--no-xvfb' in cmd:
+    use_xvfb = False
+    cmd.remove('--no-xvfb')
+
+  if sys.platform == 'linux2' and use_xvfb:
     if env.get('_CHROMIUM_INSIDE_XVFB') == '1':
       openbox_proc = None
       xcompmgr_proc = None
       try:
         # Some ChromeOS tests need a window manager.
         openbox_proc = subprocess.Popen('openbox', stdout=subprocess.PIPE,
                                         stderr=subprocess.STDOUT, env=env)
 
         # Some tests need a compositing wm to make use of transparent visuals.
         xcompmgr_proc = subprocess.Popen('xcompmgr', stdout=subprocess.PIPE,
@@ skipping 12 matching lines @@
       if xvfb_script.endswith('.pyc'):
         xvfb_script = xvfb_script[:-1]
       return subprocess.call(['xvfb-run', '-a', "--server-args=-screen 0 "
                               "1280x800x24 -ac -nolisten tcp -dpi 96",
                               xvfb_script] + cmd, env=env)
   else:
     return test_env.run_executable(cmd, env)
 
 
 def main():
-  USAGE = 'Usage: xvfb.py [command args...]'
+  USAGE = 'Usage: xvfb.py [command [--no-xvfb] args...]'
   if len(sys.argv) < 2:
     print >> sys.stderr, USAGE
     return 2
 
   # If the user still thinks the first argument is the execution directory then
   # print a friendly error message and quit.
   if os.path.isdir(sys.argv[1]):
     print >> sys.stderr, (
         'Invalid command: \"%s\" is a directory' % sys.argv[1])
     print >> sys.stderr, USAGE
     return 3
 
   return run_executable(sys.argv[1:], os.environ.copy())
 
 
 if __name__ == "__main__":
   sys.exit(main())