[Sync] Componentize SyncBackendHost{Impl,Core,Mock}.

chrome/chrome_browser.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': {
     # All .cc, .h, .m, and .mm files under browser except for:
     # * tests and mocks.
     # * code below browser/chromeos
     # * code below browser/extensions
@@ skipping 2859 matching lines @@
     ],
     'chrome_browser_supervised_user_and_themes_sources': [
       'browser/supervised_user/supervised_user_theme.cc',
       'browser/supervised_user/supervised_user_theme.h',
     ],
     'chrome_browser_sync_sources': [
       'browser/sync/chrome_sync_client.cc',
       'browser/sync/chrome_sync_client.h',
       'browser/sync/glue/extensions_activity_monitor.cc',
       'browser/sync/glue/extensions_activity_monitor.h',
-      'browser/sync/glue/sync_backend_host.cc',
-      'browser/sync/glue/sync_backend_host.h',
-      'browser/sync/glue/sync_backend_host_core.cc',
-      'browser/sync/glue/sync_backend_host_core.h',
-      'browser/sync/glue/sync_backend_host_impl.cc',
-      'browser/sync/glue/sync_backend_host_impl.h',
       'browser/sync/glue/sync_start_util.cc',
       'browser/sync/glue/sync_start_util.h',
       'browser/sync/glue/synced_tab_delegate_android.cc',
       'browser/sync/glue/synced_tab_delegate_android.h',
       'browser/sync/glue/synced_window_delegate_android.cc',
       'browser/sync/glue/synced_window_delegate_android.h',
       'browser/sync/glue/synced_window_delegates_getter_android.cc',
       'browser/sync/glue/synced_window_delegates_getter_android.h',
       'browser/sync/profile_sync_components_factory_impl.cc',
       'browser/sync/profile_sync_components_factory_impl.h',
@@ skipping 1204 matching lines @@
             '../components/components.gyp:omnibox_browser',
             '../components/components.gyp:rlz',
             '../components/components.gyp:search_engines',
             '../rlz/rlz.gyp:rlz_lib',
           ],
         },
       ],
     }],
   ],
 }