Remove unknown preferences errors in layout tests

PRESUBMIT.py

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Top-level presubmit script for Blink.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details about the presubmit API built into gcl.
 """
 
@@ skipping 290 matching lines @@
         args += ['--file', f.LocalPath()]
     checkperms = input_api.subprocess.Popen(
         args, stdout=input_api.subprocess.PIPE)
     errors = checkperms.communicate()[0].strip()
     if errors:
         return [output_api.PresubmitError(
             'checkperms.py failed.', errors.splitlines())]
     return []
 
 
+def _CheckForInvalidPreferenceError(input_api, output_api):
+    pattern = input_api.re.compile('Invalid name for preference: (.+)')
+    results = []
+
+    for f in input_api.AffectedFiles():
+        if not f.LocalPath().endswith('-expected.txt'):
+            continue
+        for line_num, line in f.ChangedContents():
+            error = pattern.search(line)
+            if error:
+                results.append(output_api.PresubmitError('Found an invalid preference %s in expected result %s:%s' % (error.group(1), f, line_num)))
+    return results
+
 def CheckChangeOnUpload(input_api, output_api):
     results = []
     results.extend(_CommonChecks(input_api, output_api))
     results.extend(_CheckStyle(input_api, output_api))
     results.extend(_CheckForPrintfDebugging(input_api, output_api))
     results.extend(_CheckForDangerousTestFunctions(input_api, output_api))
+    results.extend(_CheckForInvalidPreferenceError(input_api, output_api))
     return results
 
 
 def CheckChangeOnCommit(input_api, output_api):
     results = []
     results.extend(_CommonChecks(input_api, output_api))
     results.extend(input_api.canned_checks.CheckTreeIsOpen(
         input_api, output_api,
         json_url='http://blink-status.appspot.com/current?format=json'))
     results.extend(input_api.canned_checks.CheckChangeHasDescription(
@@ skipping 15 matching lines @@
             'mac_blink_rel': set(['defaulttests']),
             'win_blink_compile_dbg': set(['defaulttests']),
             'win_blink_rel': set(['defaulttests']),
         },
         'tryserver.chromium.gpu': {
             'linux_gpu': set(['defaulttests']),
             'mac_gpu': set(['defaulttests']),
             'win_gpu': set(['defaulttests']),
         }
     }