Split HistoryClient in two objects

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 1671 matching lines @@
     ],
     'chrome_browser_history_sources': [
       'browser/history/android/android_history_provider_service.cc',
       'browser/history/android/android_history_provider_service.h',
       'browser/history/android/android_provider_backend.cc',
       'browser/history/android/android_provider_backend.h',
       'browser/history/android/bookmark_model_sql_handler.cc',
       'browser/history/android/bookmark_model_sql_handler.h',
       'browser/history/android/sqlite_cursor.cc',
       'browser/history/android/sqlite_cursor.h',
+      'browser/history/chrome_history_backend_client.cc',
+      'browser/history/chrome_history_backend_client.h',
       'browser/history/chrome_history_client.cc',
       'browser/history/chrome_history_client.h',
       'browser/history/history_service_factory.cc',
       'browser/history/history_service_factory.h',
       'browser/history/history_tab_helper.cc',
       'browser/history/history_tab_helper.h',
       'browser/history/history_utils.cc',
       'browser/history/history_utils.h',
       'browser/history/top_sites_factory.cc',
       'browser/history/top_sites_factory.h',
@@ skipping 2358 matching lines @@
           'variables': {
             'proto_in_dir': 'browser/sync_file_system/drive_backend',
             'proto_out_dir': 'chrome/browser/sync_file_system/drive_backend',
           },
           'includes': [ '../build/protoc.gypi' ]
         },
       ],
     },],
   ],
 }