Introduce Identity Service and its initial usage

services/identity/BUILD.gn

+# Copyright 2017 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("//services/service_manager/public/cpp/service.gni")
+import("//services/service_manager/public/service_manifest.gni")
+
+source_set("lib") {
+  sources = [
+    "identity_manager.cc",
+    "identity_manager.h",
+    "identity_service.cc",
+    "identity_service.h",
+  ]
+
+  deps = [
+    "//base",
+    "//components/signin/core/account_id",
+    "//components/signin/core/browser",
+    "//services/identity/public/interfaces",
+    "//services/service_manager/public/cpp",
+    "//services/service_manager/public/interfaces",
+  ]
+}
+
+service_manifest("manifest") {
+  name = "identity"
+  source = "manifest.json"
+}