Teach run-webkit-tests to look for flag-specific platform baselines.

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

Index: third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/base.py
diff --git a/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/base.py b/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/base.py
index ef62e807f288f4d51d1ca50b30d716fdb515c3f0..80a92d76767a3454cb98a7b5b2b834f9fcc07687 100644
--- a/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/base.py
+++ b/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/base.py
@@ -1239,9 +1239,11 @@ class Port(object):
                 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', [])]
+        flag_dirs = [self._filesystem.join(self.layout_tests_dir(), 'flag-specific', flag.lstrip('-'))
+                     for flag in self.get_option('additional_driver_flag', [])]
+        return [self._filesystem.join(flag_dir, 'platform', platform_dir)
+                for platform_dir in self.FALLBACK_PATHS[self.version()]
+                for flag_dir in flag_dirs] + flag_dirs
 
     def expectations_dict(self):
         """Returns an OrderedDict of name -> expectations strings.