Add flag-specific baseline search path to run-webkit-tests.

BUG=598180

Review-Url: https://codereview.chromium.org/2182813002
Cr-Commit-Position: refs/heads/master@{#407685}

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

@@ -300,7 +300,10 @@ class Port(object):
         return [self._filesystem.join(path, suite.name) for path in self.default_baseline_search_path()]
 
     def baseline_search_path(self):
-        return self.get_option('additional_platform_directory', []) + self._compare_baseline() + self.default_baseline_search_path()
+        return (self.get_option('additional_platform_directory', []) +
+                self._flag_specific_baseline_search_path() +
+                self._compare_baseline() +
+                self.default_baseline_search_path())
 
     def default_baseline_search_path(self):
         """Return a list of absolute paths to directories to search under for
@@ -1265,6 +1268,11 @@ class Port(object):
         return [self._filesystem.join(self.layout_tests_dir(), 'FlagExpectations', flag.lstrip('-'))
                 for flag in self.get_option('additional_driver_flag', [])]
 
+    def _flag_specific_baseline_search_path(self):
+        # TODO(skobes): Baselines specific to both flag and platform?
+        return [self._filesystem.join(self.layout_tests_dir(), 'flag-specific', flag.lstrip('-'))
+                for flag in self.get_option('additional_driver_flag', [])]
+
     def expectations_dict(self):
         """Returns an OrderedDict of name -> expectations strings.
         The names are expected to be (but not required to be) paths in the filesystem.

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

@@ -211,6 +211,11 @@ class PortTest(unittest.TestCase):
             [('/tmp/local-baselines', 'fast/test-expected.txt')])
         self.assertEqual(port.baseline_path(), '/foo')
 
+        # Flag-specific baseline directory
+        port._options.additional_platform_directory = []
+        port._options.additional_driver_flag = ['--special-flag']
+        self.assertEqual(port.baseline_path(), '/mock-checkout/third_party/WebKit/LayoutTests/flag-specific/special-flag')
+
     def test_nonexistant_expectations(self):
         port = self.make_port(port_name='foo')
         port.expectations_files = lambda: ['/mock-checkout/third_party/WebKit/LayoutTests/platform/exists/TestExpectations',