Make HandleWatcher watch on the same thread if the thread is running a MessagePumpMojo.

mojo/public/cpp/application/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_public.gypi:mojo_application_base
 source_set("application") {
   sources = [
     "application_connection.h",
     "application_delegate.h",
     "application_impl.h",
@@ skipping 20 matching lines @@
 }
 
 # GYP version: mojo/mojo_base.gyp:mojo_application_chromium
 source_set("chromium") {
   sources = [
     "lib/application_runner_chromium.cc"
   ]
 
   deps = [
     ":application",
+    "//mojo/common",
     "//mojo/environment:chromium",
   ]
 }
 
 # GYP version: mojo/mojo_public.gypi:mojo_application_standalone
 source_set("standalone") {
   sources = [
     "lib/application_runner.cc"
   ]
 
   deps = [
     ":application",
     "//mojo/public/cpp/environment:standalone",
   ]
 }