[GN] Add support for generating Xcode projects.

build/config/ios/rules.gni

 # Copyright 2015 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("//build/config/mac/base_rules.gni")
 
 # Generates Info.plist files for Mac apps and frameworks.
 #
 # Arguments
 #
@@ skipping 149 matching lines @@
       ":$_bundle_data_info_plist",
     ]
 
     if (use_ios_simulator) {
       if (!defined(data_deps)) {
         data_deps = []
       }
       data_deps += [ "//testing/iossim" ]
     }
 
+    product_type = "com.apple.product-type.application"
     bundle_root_dir = "$root_out_dir/$_output_name.app"
     bundle_resources_dir = bundle_root_dir
     bundle_executable_dir = bundle_root_dir
     bundle_plugins_dir = "$bundle_root_dir/Plugins"
+    assert(product_type != "", "force use of product_type")

[brettw, 2016/05/03 20:28:14]

Ah, in that case, can you add a better comment here in case you forget to come
back and delete this line when the new build is rolled?

[sdefresne, 2016/05/03 21:08:01]

Done.

   }
 
   # TODO(crbug.com/297668):
   # - add support for codesigning,
   # - find a way to make "ninja -C out/Default base_unittests.app" work as
   #   an alias to "ninja -C out/Default base_unittests" (for convenience
   #   and compatibility with gyp),
 }
 
 # Compile a xib or storyboard file and add it to a bundle_data so that it is
@@ skipping 235 matching lines @@
                              [
                                "testonly",
                                "visibility",
                              ])
       public_deps = [
         ":$_framework_target+link",
       ]
     }
   }
 }