Add a gn implementation for //ios/public/provider/web target.

BUG=459705

Review URL: https://codereview.chromium.org/1443023002

Cr-Commit-Position: refs/heads/master@{#359812}

BUILD.gn

@@ -205,6 +205,7 @@ group("both_gn_and_gyp") {
   } else {
     deps += [
       "//ios/net:ios_net_unittests",
+      "//ios/public/provider/web",
       "//ios/testing:ocmock_support_unittest",
       "//ios/web:ios_web_unittests",
     ]

ios/provider/ios_provider_web.gyp

@@ -7,6 +7,7 @@
    },
   'targets': [
     {
+      # GN version: //ios/public/provider/web
       'target_name': 'ios_provider_web',
       'type': 'static_library',
       'include_dirs': [

ios/public/provider/web/BUILD.gn

@@ -0,0 +1,21 @@
+# 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.
+
+source_set("web") {
+  sources = [
+    "web_controller_provider.h",
+    "web_controller_provider.mm",
+    "web_ui_ios.h",
+    "web_ui_ios_controller.cc",
+    "web_ui_ios_controller.h",
+    "web_ui_ios_controller_factory.h",
+    "web_ui_ios_message_handler.cc",
+    "web_ui_ios_message_handler.h",
+  ]
+
+  deps = [
+    "//base",
+    "//ios/web",
+  ]
+}