Add prefs UI tests for Incognito exceptions for new Settings UI.

chrome/test/pyautolib/pyauto.py

Index: chrome/test/pyautolib/pyauto.py
===================================================================
--- chrome/test/pyautolib/pyauto.py	(revision 124707)
+++ chrome/test/pyautolib/pyauto.py	(working copy)
@@ -1294,7 +1294,7 @@
         self._SendJSONRequest(-1, json.dumps(cmd_dict),
                               self.action_max_timeout_ms()))
 
-  def SetPrefs(self, path, value):
+  def SetPrefs(self, path, value, windex=0):
     """Set preference for the given path.
 
     Preferences are stored by Chromium as a hierarchical dictionary.
@@ -1315,10 +1315,11 @@
              The user has to ensure that the right value is specified for the
              right key. It's useful to dump the preferences first to determine
              what type is expected for a particular preference path.
+      windex: window index to work on. Defaults to 0 (first window).
     """
     cmd_dict = {
       'command': 'SetPrefs',
-      'windex': 0,
+      'windex': windex,
       'path': path,
       'value': value,
     }