fix virtual_test_suites() for browser_test ports

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

Index: Tools/Scripts/webkitpy/layout_tests/port/port_testcase.py
diff --git a/Tools/Scripts/webkitpy/layout_tests/port/port_testcase.py b/Tools/Scripts/webkitpy/layout_tests/port/port_testcase.py
index 7b1dfe165df0d1b3df2fa3c90ebd6c940a3a7457..5e57c3d5d7bc33d81b544f58efbce8eaaa42ec85 100644
--- a/Tools/Scripts/webkitpy/layout_tests/port/port_testcase.py
+++ b/Tools/Scripts/webkitpy/layout_tests/port/port_testcase.py
@@ -39,6 +39,7 @@ import unittest
 from webkitpy.common.system.executive_mock import MockExecutive, MockExecutive2
 from webkitpy.common.system.filesystem_mock import MockFileSystem
 from webkitpy.common.system.outputcapture import OutputCapture
+from webkitpy.common.system.systemhost import SystemHost
 from webkitpy.common.system.systemhost_mock import MockSystemHost
 from webkitpy.layout_tests.models import test_run_results
 from webkitpy.layout_tests.port.base import Port, TestConfiguration
@@ -465,3 +466,9 @@ class PortTestCase(unittest.TestCase):
     def test_additional_platform_directory(self):
         port = self.make_port(options=MockOptions(additional_platform_directory=['/tmp/foo']))
         self.assertEqual(port.baseline_search_path()[0], '/tmp/foo')
+
+    def test_virtual_test_suites(self):
+        port = self.make_port(host=SystemHost())
+
+        # Test that this returns *something* and doesn't raise an exception.
+        self.assertNotEqual(port.virtual_test_suites(), None)