Don't use --enable-software-compositing flag in virtual test.

Tools/Scripts/webkitpy/layout_tests/port/base.py

 # Copyright (C) 2010 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 # copyright notice, this list of conditions and the following disclaimer
@@ skipping 1523 matching lines @@
                              ['--enable-threaded-compositing']),
             VirtualTestSuite('threaded',
                              'compositing/webgl',
                              ['--enable-threaded-compositing']),
             VirtualTestSuite('gpu',
                              'fast/hidpi',
                              ['--force-compositing-mode']),
             VirtualTestSuite('softwarecompositing',
                              'compositing',
                              ['--disable-gpu',
-                              '--enable-software-compositing',
                               '--disable-gpu-compositing'],
                              use_legacy_naming=True),
             VirtualTestSuite('deferred',
                              'fast/images',
                              ['--enable-deferred-image-decoding', '--enable-per-tile-painting', '--force-compositing-mode']),
             VirtualTestSuite('deferred',
                              'inspector/timeline',
                              ['--enable-deferred-image-decoding', '--enable-per-tile-painting', '--force-compositing-mode']),
             VirtualTestSuite('gpu/compositedscrolling/overflow',
                              'compositing/overflow',
@@ skipping 204 matching lines @@
             if name.find('/') != -1:
                 _log.error("Virtual test suites names cannot contain /'s: %s" % name)
                 return
             self.name = 'virtual/' + name + '/' + base
         self.base = base
         self.args = args
         self.tests = tests or set()
 
     def __repr__(self):
         return "VirtualTestSuite('%s', '%s', %s)" % (self.name, self.base, self.args)