Add gn implementation of //ios/web/shell:ios_web_shell.

ios/web/ios_web_shell.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.
 
 {
   'variables': {
     'chromium_code': 1,
    },
   'targets': [
     {
+      # GN version: //ios/web/shell:ios_web_shell
       'target_name': 'ios_web_shell',
       'type': 'executable',
       'mac_bundle': 1,
       'include_dirs': [
         '../..',
       ],
       'dependencies': [
         'ios_web.gyp:ios_web',
         'ios_web.gyp:ios_web_app',
         '../../base/base.gyp:base',
@@ skipping 37 matching lines @@
         'libraries': [
           '$(SDKROOT)/System/Library/Frameworks/CoreGraphics.framework',
           '$(SDKROOT)/System/Library/Frameworks/CoreFoundation.framework',
           '$(SDKROOT)/System/Library/Frameworks/Foundation.framework',
           '$(SDKROOT)/System/Library/Frameworks/UIKit.framework',
         ],
       },
     },
   ],
 }