Introduce proximity_auth component.

components/proximity_auth/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.
+
+static_library("proximity_auth") {
+  sources = [
+    "proximity_auth_system.cc",
+    "proximity_auth_system.h",
+    "remote_device.h",
+  ]
+}
+
+test("proximity_auth_unittests") {
+  sources = [
+    "proximity_auth_system_unittest.cc",
+    "run_all_unittests.cc",
+  ]
+
+  deps = [
+    ":proximity_auth",
+    "//base/test:test_support",
+    "//testing/gtest",
+  ]
+}