Split out the extensions gin::Runner implementation into a separate class.

extensions/BUILD.gn

 # 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.
 
 import("//tools/grit/grit_rule.gni")
 import("//tools/grit/repack.gni")
 
 assert(enable_extensions)
 
 # GYP version: extensions/extensions_resources.gyp:extensions_resources
@@ skipping 232 matching lines @@
       "renderer/api_test_base_unittest.cc",
       "renderer/event_unittest.cc",
       "renderer/json_schema_unittest.cc",
       "renderer/messaging_utils_unittest.cc",
       "renderer/module_system_test.cc",
       "renderer/module_system_test.h",
       "renderer/module_system_unittest.cc",
       "renderer/mojo/keep_alive_client_unittest.cc",
       "renderer/safe_builtins_unittest.cc",
       "renderer/script_context_set_unittest.cc",
+      "renderer/script_context_unittest.cc",
       "renderer/utils_unittest.cc",
       "test/extensions_unittests_main.cc",
     ]
 
     deps = [
       ":extensions_resources",
       ":shell_and_test_pak",
       ":test_support",
       "//base",
       "//base:prefs_test_support",
@@ skipping 12 matching lines @@
       "//testing/gmock",
       "//testing/gtest",
       "//third_party/leveldatabase",
     ]
 
     if (is_win) {
       deps += [ "//base/allocator" ]
     }
   }
 }