In run-webkit-tests, start xvfb if necessary.

third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/linux_unittest.py

Index: third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/linux_unittest.py
diff --git a/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/linux_unittest.py b/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/linux_unittest.py
index fe363f73c44d767964611998b915a8c11137a37d..e62e030ecf3d1501de23567d7087be83b9a53ba0 100644
--- a/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/linux_unittest.py
+++ b/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/linux_unittest.py
@@ -114,3 +114,30 @@ class LinuxPortTest(port_testcase.PortTestCase):
         port.clean_up_test_run()
         self.assertEqual(port.host.environ['HOME'], '/home/user')
         self.assertFalse(port.host.filesystem.exists(temp_home_dir))
+
+    def test_xvfb_started_no_display(self):
+        port = self.make_port()
+        port.host.environ['DISPLAY'] = ''
+        port.setup_test_run()
+        self.assertEqual(
+            port.host.executive.calls,
+            [['Xvfb', ':20', '-screen', '0', '1280x800x24', '-ac', '-dpi', '96']])
+
+    def test_xvfb_started_with_display(self):
+        port = self.make_port()
+        port.host.environ['DISPLAY'] = ':0'
+        port.host.executive = MockExecutive(exit_code=0)
+        port.setup_test_run()
+        self.assertEqual(port.host.executive.calls, [['xdpyinfo', '-display', ':0']])
+
+    def test_xvfb_started_with_display_set_but_no_x_server(self):
+        port = self.make_port()
+        port.host.environ['DISPLAY'] = ':0'
+        port.host.executive = MockExecutive(exit_code=1)
+        port.setup_test_run()
+        self.assertEqual(
+            port.host.executive.calls,
+            [
+                ['xdpyinfo', '-display', ':0'],
+                ['Xvfb', ':0', '-screen', '0', '1280x800x24', '-ac', '-dpi', '96']
+            ])