Extract requestMediaKeySystemAccess() algorithm.

media/blink/media_blink.gyp

 # Copyright 2014 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.
 
 {
   'targets': [
     {
       # GN version: //media/blink
       'target_name': 'media_blink',
       'type': '<(component)',
@@ skipping 25 matching lines @@
         'buffered_resource_loader.h',
         'cache_util.cc',
         'cache_util.h',
         'cdm_result_promise.h',
         'cdm_result_promise_helper.cc',
         'cdm_result_promise_helper.h',
         'cdm_session_adapter.cc',
         'cdm_session_adapter.h',
         'encrypted_media_player_support.cc',
         'encrypted_media_player_support.h',
+        'key_system_config_selector.cc',
+        'key_system_config_selector.h',
         'new_session_cdm_result_promise.cc',
         'new_session_cdm_result_promise.h',
         'texttrack_impl.cc',
         'texttrack_impl.h',
         'video_frame_compositor.cc',
         'video_frame_compositor.h',
         'webaudiosourceprovider_impl.cc',
         'webaudiosourceprovider_impl.h',
         'webcontentdecryptionmodule_impl.cc',
         'webcontentdecryptionmodule_impl.h',
@@ skipping 59 matching lines @@
         'mock_weburlloader.h',
         'run_all_unittests.cc',
         'test_response_generator.cc',
         'test_response_generator.h',
         'video_frame_compositor_unittest.cc',
         'webaudiosourceprovider_impl_unittest.cc',
       ],
     },
   ]
 }