Convert Connect apptest to a unittest

mojo/shell/public/cpp/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.
 
 # GYP version: mojo/mojo_base.gyp:mojo_application_base
 source_set("cpp") {
   public_deps = [
     ":init_commandline",
     ":sources",
   ]
@@ skipping 55 matching lines @@
     "lib/init_commandline.cc",
   ]
 }
 
 source_set("test_support") {
   testonly = true
   sources = [
     "application_test_base.h",
     "lib/application_test_base.cc",
     "lib/application_test_main.cc",
+    "lib/shell_test.cc",
+    "shell_test.h",
   ]
 
   public_deps = [
     ":cpp",
     "//testing/gtest",
   ]
 
   deps = [
     "//base",
     "//base/test:test_support",
     "//mojo/logging",
     "//mojo/public/cpp/bindings",
     "//mojo/public/cpp/environment",
     "//mojo/public/cpp/system",
+    "//mojo/shell/background:lib",
     "//mojo/shell/public/interfaces:interfaces_cpp_sources",
   ]
 
   data_deps = []
 }