Convert enable_pre_sync_backup flag to new flags system.

chrome/chrome_tests_unit.gypi

 # Copyright 2012 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': {
     'chrome_unit_tests_sources': [
       # histograms.xml is analyzed by AboutFlagsHistogramTest, so this
       # dependency is needed to make commit bots run unit_tests on
       # histograms.xml changes.
       '../tools/metrics/histograms/histograms.xml',
@@ skipping 2189 matching lines @@
         '../net/net.gyp:net_test_support',
         '../sync/sync.gyp:test_support_sync_api',
         '../sync/sync.gyp:test_support_sync_core',
         '../sync/sync.gyp:test_support_sync_internal_api',
         '../testing/gmock.gyp:gmock',
         '../testing/gtest.gyp:gtest',
         'test_support_common',
         'test_support_unit',
         # 3) anything tests directly depend on
         '../components/components.gyp:generate_version_info',
+        '../components/components.gyp:sync_driver_features',
         '../courgette/courgette.gyp:courgette_lib',
         '../google_apis/google_apis.gyp:google_apis',
         '../skia/skia.gyp:skia',
         '../third_party/cacheinvalidation/cacheinvalidation.gyp:cacheinvalidation',
         '../third_party/icu/icu.gyp:icui18n',
         '../third_party/icu/icu.gyp:icuuc',
         '../third_party/libxml/libxml.gyp:libxml',
         '../ui/base/ui_base.gyp:ui_base_test_support',
         '../ui/gfx/gfx.gyp:gfx_test_support',
         '../ui/resources/ui_resources.gyp:ui_resources',
@@ skipping 780 matching lines @@
               'dependencies': [
                 '../tools/xdisplaycheck/xdisplaycheck.gyp:xdisplaycheck',
               ],
             }],
           ],
         },
       ],
     }],
   ],  # 'conditions'
 }