Introduce Identity Service and its initial usage

services/identity/public/interfaces/BUILD.gn

Index: services/identity/public/interfaces/BUILD.gn
diff --git a/services/identity/public/interfaces/BUILD.gn b/services/identity/public/interfaces/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..f2e15ffe96b1749627a2cf8444fe5d0441e00fd4
--- /dev/null
+++ b/services/identity/public/interfaces/BUILD.gn
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+# Copyright 2016 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("//mojo/public/tools/bindings/mojom.gni")
+
+mojom("interfaces") {
+  sources = [
+    "identity_manager.mojom",
+  ]
+
+  public_deps = [
+    ":constants",
+    "//components/signin/public/interfaces",
+  ]
+}
+
+mojom("constants") {
+  sources = [
+    "constants.mojom",
+  ]
+}