Add an additional content_shell per worker for running virtual tests.

Tools/Scripts/webkitpy/layout_tests/controllers/layout_test_runner_unittest.py

Index: Tools/Scripts/webkitpy/layout_tests/controllers/layout_test_runner_unittest.py
diff --git a/Tools/Scripts/webkitpy/layout_tests/controllers/layout_test_runner_unittest.py b/Tools/Scripts/webkitpy/layout_tests/controllers/layout_test_runner_unittest.py
index 9ce796af34bf816f026c458cf44749839f2d8c57..6bdd7597dfcc271cf07a785f1e19befef69ab70d 100644
--- a/Tools/Scripts/webkitpy/layout_tests/controllers/layout_test_runner_unittest.py
+++ b/Tools/Scripts/webkitpy/layout_tests/controllers/layout_test_runner_unittest.py
@@ -32,7 +32,7 @@ import unittest
 from webkitpy.common.host_mock import MockHost
 from webkitpy.common.system.systemhost_mock import MockSystemHost
 from webkitpy.layout_tests import run_webkit_tests
-from webkitpy.layout_tests.controllers.layout_test_runner import LayoutTestRunner, Sharder, TestRunInterruptedException
+from webkitpy.layout_tests.controllers.layout_test_runner import DriverHandler, LayoutTestRunner, Sharder, TestRunInterruptedException
 from webkitpy.layout_tests.models import test_expectations
 from webkitpy.layout_tests.models import test_failures
 from webkitpy.layout_tests.models.test_run_results import TestRunResults
@@ -156,6 +156,36 @@ class LayoutTestRunnerTests(unittest.TestCase):
         self.assertEqual(1, run_results.unexpected)
 
 
+class DriverHandlerTests(unittest.TestCase):
+    def _create_driver_handler(self):
+        port = TestPort(MockSystemHost())
+        return DriverHandler("test_driver", 1, "test_worker", port)
+
+    def test_init(self):
+        self.assertFalse(self._create_driver_handler().driver)
+
+    def test_prepare(self):
+        driver_handler = self._create_driver_handler()
+        driver_handler.prepare()
+        self.assertTrue(driver_handler.driver)
+
+    def test_is_prepared(self):
+        driver_handler = self._create_driver_handler()
+        self.assertFalse(driver_handler.is_prepared())
+        driver_handler.prepare()
+        self.assertTrue(driver_handler.is_prepared())
+        driver_handler.kill()
+        self.assertFalse(driver_handler.is_prepared())
+
+    def test_kill(self):
+        driver_handler = self._create_driver_handler()
+        driver_handler.kill()
+        self.assertFalse(driver_handler.driver)
+        driver_handler.prepare()
+        driver_handler.kill()
+        self.assertFalse(driver_handler.driver)
+
+
 class SharderTests(unittest.TestCase):
 
     test_list = [