Add gn implementation for //components/keyed_service/ios.

components/keyed_service/ios/BUILD.gn

Index: components/keyed_service/ios/BUILD.gn
diff --git a/components/keyed_service/ios/BUILD.gn b/components/keyed_service/ios/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..2413c84588d69d9fc38e1dc0d8b93dc8b31c884b
--- /dev/null
+++ b/components/keyed_service/ios/BUILD.gn
@@ -0,0 +1,25 @@
+# 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("ios") {
+  sources = [
+    "browser_state_context_converter.cc",
+    "browser_state_context_converter.h",
+    "browser_state_dependency_manager.cc",
+    "browser_state_dependency_manager.h",
+    "browser_state_keyed_service_factory.cc",
+    "browser_state_keyed_service_factory.h",
+    "refcounted_browser_state_keyed_service_factory.cc",
+    "refcounted_browser_state_keyed_service_factory.h",
+  ]
+
+  deps = [
+    "//base",
+    "//base/third_party/dynamic_annotations",
+    "//components/keyed_service/core",
+    "//ios/web",
+  ]
+
+  defines = [ "KEYED_SERVICE_IMPLEMENTATION" ]
+}