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.
 
-source_set("crx_file") {
+static_library("proximity_auth") {
   sources = [
-    "constants.h",
-    "crx_file.cc",
-    "crx_file.h",
-    "id_util.cc",
-    "id_util.h",
+    "proximity_auth_system.cc",
+    "proximity_auth_system.h",
+    "remote_device.h",
   ]
 
   deps = [
     "//base",
   ]
 }
 
 source_set("unit_tests") {
   sources = [
-    "id_util_unittest.cc",
+    "proximity_auth_system_unittest.cc",
   ]
 
   deps = [
-    ":crx_file",
+    ":proximity_auth",
+    "//base/test:test_support",
     "//testing/gtest",
   ]
 }