Introduce ScriptInjection in extensions/renderer to inject UserScripts

extensions/extensions.gyp

 # Copyright 2013 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': {
     'chromium_code': 1,
   },
   'targets': [
     {
@@ skipping 515 matching lines @@
         'renderer/safe_builtins.h',
         'renderer/send_request_natives.cc',
         'renderer/send_request_natives.h',
         'renderer/set_icon_natives.cc',
         'renderer/set_icon_natives.h',
         'renderer/scoped_persistent.h',
         'renderer/script_context.cc',
         'renderer/script_context.h',
         'renderer/script_context_set.cc',
         'renderer/script_context_set.h',
+        'renderer/script_injection.cc',
+        'renderer/script_injection.h',
         'renderer/static_v8_external_ascii_string_resource.cc',
         'renderer/static_v8_external_ascii_string_resource.h',
         'renderer/test_features_native_handler.cc',
         'renderer/test_features_native_handler.h',
         'renderer/user_gestures_native_handler.cc',
         'renderer/user_gestures_native_handler.h',
         'renderer/user_script_scheduler.cc',
         'renderer/user_script_scheduler.h',
         'renderer/user_script_slave.cc',
         'renderer/user_script_slave.h',
@@ skipping 85 matching lines @@
         'test/test_extensions_client.cc',
         'test/test_extensions_client.h',
         'test/test_permission_message_provider.cc',
         'test/test_permission_message_provider.h',
         'test/test_permissions_provider.cc',
         'test/test_permissions_provider.h',
       ],
     },
   ]
 }