allow usage of transparent visuals when using xvfb

testing/scripts/run_telemetry_as_googletest.py

 #!/usr/bin/env python
 # Copyright 2015 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 isolate bundled Telemetry unittests.
 
 This script attempts to emulate the contract of gtest-style tests
 invoked via recipes. The main contract is that the caller passes the
 argument:
@@ skipping 23 matching lines @@
 
 def main():
   parser = argparse.ArgumentParser()
   parser.add_argument(
       '--isolated-script-test-output', type=argparse.FileType('w'),
       required=True)
   parser.add_argument('--xvfb', help='Start xvfb.', action='store_true')
   args, rest_args = parser.parse_known_args()
   xvfb_proc = None
   openbox_proc = None
+  xcompmgr_proc = None
   env = os.environ.copy()
   if args.xvfb and xvfb.should_start_xvfb(env):
-    xvfb_proc, openbox_proc = xvfb.start_xvfb(env=env, build_dir='.')
-    assert xvfb_proc and openbox_proc, 'Failed to start xvfb'
+    xvfb_proc, openbox_proc, xcompmgr_proc = xvfb.start_xvfb(env=env,
+                                                             build_dir='.')
+    assert xvfb_proc and openbox_proc and xcompmgr_proc, 'Failed to start xvfb'
   try:
     with common.temporary_file() as tempfile_path:
       rc = common.run_command([sys.executable] + rest_args + [
         '--write-full-results-to', tempfile_path,
       ], env=env)
       with open(tempfile_path) as f:
         results = json.load(f)
       parsed_results = common.parse_common_test_results(results,
                                                         test_separator='.')
       failures = parsed_results['unexpected_failures']
 
       json.dump({
           'valid': bool(rc <= common.MAX_FAILURES_EXIT_STATUS and
                         ((rc == 0) or failures)),
           'failures': failures.keys(),
       }, args.isolated_script_test_output)
 
     return rc
   finally:
     xvfb.kill(xvfb_proc)
     xvfb.kill(openbox_proc)
+    xvfb.kill(xcompmgr_proc)
 
 
 
 # This is not really a "script test" so does not need to manually add
 # any additional compile targets.
 def main_compile_targets(args):
   json.dump([], args.output)
 
 
 if __name__ == '__main__':
   # Conform minimally to the protocol defined by ScriptTest.
   if 'compile_targets' in sys.argv:
     funcs = {
       'run': None,
       'compile_targets': main_compile_targets,
     }
     sys.exit(common.run_script(sys.argv[1:], funcs))
   sys.exit(main())