Use xvfb for the ozone linux tests

tools/mb/mb.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.
 
 """MB - the Meta-Build wrapper around GYP and GN
 
 MB is a wrapper script for GYP and GN that can be used to generate build files
 for sets of canned configurations and analyze them.
 """
@@ skipping 1041 matching lines @@
       self.Print('analyze output:')
       self.PrintJSON(outp)
       self.Print()
 
     return ret
 
   def GetIsolateCommand(self, target, vals):
     isolate_map = self.ReadIsolateMap()
 
     android = 'target_os="android"' in vals['gn_args']
-    ozone = 'use_ozone=true' in vals['gn_args']
-    chromeos = 'target_os="chromeos"' in vals['gn_args']
 
     # This should be true if tests with type='windowed_test_launcher' are
     # expected to run using xvfb. For example, Linux Desktop, X11 CrOS and
-    # Ozone CrOS builds.
+    # Ozone CrOS builds. Note that one Ozone build can be used to run differen
+    # backends. Currently, tests are executed for the headless and X11 backends
+    # and both can run under Xvfb.
+    # TODO(tonikitoo,msisov,fwang): Find a way to run tests for the Wayland
+    # backend.
     use_xvfb = (self.platform == 'linux2' and
-               not android and
-               ((not ozone) or (ozone and chromeos)))
+                       not android)
 
     asan = 'is_asan=true' in vals['gn_args']
     msan = 'is_msan=true' in vals['gn_args']
     tsan = 'is_tsan=true' in vals['gn_args']
 
     test_type = isolate_map[target]['type']
 
     executable = isolate_map[target].get('executable', target)
     executable_suffix = '.exe' if self.platform == 'win32' else ''
 
@@ skipping 479 matching lines @@
   # Then check to see if the arg contains any metacharacters other than
   # double quotes; if it does, quote everything (including the double
   # quotes) for safety.
   if any(a in UNSAFE_FOR_CMD for a in arg):
     arg = ''.join('^' + a if a in ALL_META_CHARS else a for a in arg)
   return arg
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv[1:]))