Mock the LinkDoctor for tests. Should greatly decrease ErrorPage test flakiness.

chrome/chrome.gyp

 # Copyright (c) 2009 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.
 
 {
   'variables': {
     'chromium_code': 1,
 
     # Define the common dependencies that contain all the actual
     # Chromium functionality.  This list gets pulled in below by
@@ skipping 1566 matching lines @@
         'browser/net/url_fetcher_protect.cc',
         'browser/net/url_fetcher_protect.h',
         'browser/net/url_fixer_upper.cc',
         'browser/net/url_fixer_upper.h',
         'browser/net/url_request_failed_dns_job.cc',
         'browser/net/url_request_failed_dns_job.h',
         # TODO:  These should be moved to test_support (see below), but
         # are currently used by production code in automation_provider.cc.
         'browser/net/url_request_mock_http_job.cc',
         'browser/net/url_request_mock_http_job.h',
+        'browser/net/url_request_mock_link_doctor_job.cc',
+        'browser/net/url_request_mock_link_doctor_job.h',
         'browser/net/url_request_mock_util.cc',
         'browser/net/url_request_mock_util.h',
         'browser/net/url_request_slow_download_job.cc',
         'browser/net/url_request_slow_download_job.h',
         'browser/net/url_request_slow_http_job.cc',
         'browser/net/url_request_slow_http_job.h',
         'browser/net/url_request_tracking.cc',
         'browser/net/url_request_tracking.h',
         'browser/omnibox_search_hint.cc',
         'browser/omnibox_search_hint.h',
@@ skipping 5004 matching lines @@
               'dependencies': [
                 '../third_party/pthreads-win32/pthreads.gyp:pthreads',
               ],
             }],
           ],
         },
       ],  # targets when chrome_personalization==1 and use_syncapi_stub==0
     }],
   ],  # 'conditions'
 }