Implement main blink target in GN.

Source/bindings/modules/v8/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("//third_party/WebKit/Source/bindings/modules/v8/generated.gni")
 import("//third_party/WebKit/Source/bindings/scripts/scripts.gni")
 import("//third_party/WebKit/Source/modules/modules.gni")
 
+visibility = "//third_party/WebKit/*"
+
 # bindings_modules_generated in modules/v8/generated.gyp
 group("bindings_modules_generated") {
   deps = [
     ":bindings_modules_generated_aggregate",
     ":bindings_modules_generated_individual",
   ]
 }
 
 # bindings_modules_generated_aggregate in modules/v8/generated.gyp
 aggregate_generated_bindings("bindings_modules_generated_aggregate") {
   sources = modules_idl_files
   component_dir = "modules"
   outputs = bindings_modules_generated_aggregate_files
 }
 
 # bindings_modules_generated_individual in modules/v8/generated.gyp
 idl_compiler("bindings_modules_generated_individual") {
   # Note in GYP this is modules_interface_idl_files but this variable is just
   # defined to modules_idl_files.
   sources = modules_idl_files
   output_dir = bindings_modules_v8_output_dir
 }