[SP] Add flag to explicitly disable slimming paint by default when running layout tests.

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 205 matching lines @@
         self._test_configuration = None
         self._reftest_list = {}
         self._results_directory = None
         self._virtual_test_suites = None
 
     def buildbot_archives_baselines(self):
         return True
 
     def additional_driver_flag(self):
         if self.driver_name() == self.CONTENT_SHELL_NAME:
-            return ['--run-layout-test']
+            return ['--run-layout-test', '--disable-slimming-paint']
         return []
 
     def supports_per_test_timeout(self):
         return False
 
     def default_pixel_tests(self):
         return True
 
     def default_smoke_test_only(self):
         return False
@@ skipping 1526 matching lines @@
 class PhysicalTestSuite(object):
     def __init__(self, base, args, reference_args=None):
         self.name = base
         self.base = base
         self.args = args
         self.reference_args = args if reference_args is None else reference_args
         self.tests = set()
 
     def __repr__(self):
         return "PhysicalTestSuite('%s', '%s', %s, %s)" % (self.name, self.base, self.args, self.reference_args)