Get mojo_shell building inside chromium checkout.

mojo/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.
 
 import("//build/config/ui.gni")
 
 group("mojo") {
   # Meta-target, don't link into production code.
   testonly = true
   deps = [
     ":tests",
     "//mojo/common",
     "//mojo/services",
     "//third_party/mojo/src/mojo/public",
   ]
 
   if (is_android) {
     deps += [ "//mojo/android" ]
   }
+
+  if (!is_component_build) {
+    deps += [ "//mojo/shell" ]
+  }
 }
 
 group("tests") {
   testonly = true
   deps = [
     "//mojo/common:mojo_common_unittests",
     "//mojo/converters/surfaces/tests:mojo_surfaces_lib_unittests",
     "//third_party/mojo/src/mojo/edk/js/test:js_unittests",
     "//third_party/mojo/src/mojo/edk/system:mojo_message_pipe_perftests",
     "//third_party/mojo/src/mojo/edk/system:mojo_system_unittests",
     "//third_party/mojo/src/mojo/edk/test:mojo_public_application_unittests",
     "//third_party/mojo/src/mojo/edk/test:mojo_public_bindings_unittests",
     "//third_party/mojo/src/mojo/edk/test:mojo_public_environment_unittests",
     "//third_party/mojo/src/mojo/edk/test:mojo_public_system_perftests",
     "//third_party/mojo/src/mojo/edk/test:mojo_public_system_unittests",
     "//third_party/mojo/src/mojo/edk/test:mojo_public_utility_unittests",
   ]
 }