Add LayoutTests/FlagExpectations directory for flag-specific expectations.

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

Index: third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/base_unittest.py
diff --git a/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/base_unittest.py b/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/base_unittest.py
index b5ee6ae62d00d38f8a012720f1b6d34ad50831d3..26399ef354558d6c1e51c12ce60d8c1134f6b2f3 100644
--- a/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/base_unittest.py
+++ b/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/base_unittest.py
@@ -230,6 +230,7 @@ class PortTest(unittest.TestCase):
             '/tmp/additional-expectations-1.txt', 'content1\n')
         port._filesystem.write_text_file(
             '/tmp/additional-expectations-2.txt', 'content2\n')
+        port._filesystem.write_text_file('/mock-checkout/third_party/WebKit/LayoutTests/FlagExpectations/special-flag', 'content3')
 
         self.assertEqual('\n'.join(port.expectations_dict().values()), '')
 
@@ -245,6 +246,9 @@ class PortTest(unittest.TestCase):
             '/tmp/additional-expectations-1.txt', '/tmp/additional-expectations-2.txt']
         self.assertEqual('\n'.join(port.expectations_dict().values()), 'content1\n\ncontent2\n')
 
+        port._options.additional_driver_flag = ['--special-flag']
+        self.assertEqual('\n'.join(port.expectations_dict().values()), 'content3\ncontent1\n\ncontent2\n')
+
     def test_additional_env_var(self):
         port = self.make_port(options=optparse.Values({'additional_env_var': ['FOO=BAR', 'BAR=FOO']}))
         self.assertEqual(port.get_option('additional_env_var'), ['FOO=BAR', 'BAR=FOO'])