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

Tools/Scripts/webkitpy/layout_tests/port/driver_unittest.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 113 matching lines @@
         self.assertEqual(content_block.content_type, 'image/png')
         self.assertEqual(content_block.content_hash, 'actual')
         self.assertEqual(content_block.encoding, 'base64')
         self.assertEqual(content_block.content, 'MTIzNDU2NzgK')
         self.assertEqual(content_block.decoded_content, '12345678\n')
 
     def test_no_timeout(self):
         port = TestWebKitPort()
         port._config.build_directory = lambda configuration: '/mock-checkout/out/' + configuration
         driver = Driver(port, 0, pixel_tests=True, no_timeout=True)
-        self.assertEqual(driver.cmd_line(True, []), ['/mock-checkout/out/Release/content_shell', '--no-timeout', '--run-layout-test', '-'])
+        self.assertEqual(driver.cmd_line(True, []), ['/mock-checkout/out/Release/content_shell', '--no-timeout', '--run-layout-test', '--disable-slimming-paint', '-'])
 
     def test_check_for_driver_crash(self):
         port = TestWebKitPort()
         driver = Driver(port, 0, pixel_tests=True)
 
         class FakeServerProcess(object):
             def __init__(self, crashed):
                 self.crashed = crashed
 
             def pid(self):
@@ skipping 92 matching lines @@
         last_tmpdir = port._filesystem.last_tmpdir
         driver._start(True, [])
         self.assertFalse(port._filesystem.isdir(last_tmpdir))
 
     def test_start_actually_starts(self):
         port = TestWebKitPort()
         port._server_process_constructor = MockServerProcess
         driver = Driver(port, 0, pixel_tests=True)
         driver.start(True, [], None)
         self.assertTrue(driver._server_process.started)