Add a test that verifies the DNS prefetching preference

chrome/test/functional/prefs.py

Index: chrome/test/functional/prefs.py
===================================================================
--- chrome/test/functional/prefs.py	(revision 50541)
+++ chrome/test/functional/prefs.py	(working copy)
@@ -120,6 +120,14 @@
     if self.IsMac():
       self.assertTrue(self.GetPrefsInfo().Prefs(pyauto.kShowPageOptionsButtons))
 
+  def testDnsPrefectchingEnabledPref(self):
+    """Verify DNS prefetching pref"""
+    # Assert default
+    self.assertTrue(self.GetPrefsInfo().Prefs(pyauto.kDnsPrefetchingEnabled))
+    self.SetPrefs(pyauto.kDnsPrefetchingEnabled, False)
+    self.RestartBrowser(clear_profile=False)
+    self.assertFalse(self.GetPrefsInfo().Prefs(pyauto.kDnsPrefetchingEnabled))
+
   def testHomepagePrefs(self):
     """Verify homepage prefs."""
     # "Use the New Tab page"