Disabled few flaky tests on Mac

PYAUTO_TESTS

 # Copyright (c) 2011 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.
 #
 # This file lists the pyauto tests that run as a part of the functional test
 # suite.
 #
 # Tests can be enabled on a per-platform basis. Tests not listed here will
 # not be run.
 #
@@ skipping 176 matching lines @@
       # crbug.com/75724
       '-downloads.DownloadsTest.testDeclineDangerousDownload',
       # crbug.com/75724
       '-downloads.DownloadsTest.testSaveDangerousFile',
       '-instant.InstantTest.testInstantNavigation',  # crbug.com/69090
       # crbug.com/66072
       '-notifications.NotificationsTest.testNotificationOrderAfterClosingOne',
       '-ntp.NTPTest.testLaunchAppNewWindow',  # crbug.com/79812
       # crbug.com/70437
       '-omnibox.OmniboxTest.testHistoryResult',
+      # crbug.com/91617
+      '-omnibox.OmniboxTest.testContentHistory',
+      '-omnibox.OmniboxTest.testOmniboxSearchHistory',      
       # Keychain popups make autofill/password tests difficult: crbug.com/49378
       '-passwords',
       # crbug.com/79263
       '-popups.PopupsTest.testPopupsLaunchUponBrowserBackButton',
       # crbug.com/69619
       '-search_engines.SearchEnginesTest.testDiscoverSearchEngine',
       # Keychain popups make sync tests difficult on Mac.  crbug.com/49378
       '-sync',
       # crbug.com/87837
       '-plugins.PluginsTest.testBlockPluginException',
@@ skipping 268 matching lines @@
 
   # HTML5 media functional tests.
   'AV_FUNC': {
      'linux': [
        'media.media_event_simple_action',
        'media.media_event_simple_test',
        'media.media_event_track',
      ],
   },
 }