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

mojo/public/cpp/application/lib/application_runner_chromium.cc

 // 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.
 
 #include "mojo/public/cpp/application/application_runner_chromium.h"
 
 #include "base/at_exit.h"
 #include "base/command_line.h"
+#include "base/memory/scoped_ptr.h"
 #include "base/message_loop/message_loop.h"
+#include "mojo/common/message_pump_mojo.h"
 #include "mojo/public/cpp/application/application_delegate.h"
 #include "mojo/public/cpp/application/application_impl.h"
 
 namespace mojo {
 
 // static
 void ApplicationImpl::Terminate() {
   if (base::MessageLoop::current()->is_running())
     base::MessageLoop::current()->Quit();
 }
 
 ApplicationRunnerChromium::ApplicationRunnerChromium(
     ApplicationDelegate* delegate)
     : delegate_(scoped_ptr<ApplicationDelegate>(delegate)),
-      message_loop_type_(base::MessageLoop::TYPE_DEFAULT) {}
+      message_loop_type_(base::MessageLoop::TYPE_CUSTOM),
+      has_run_(false) {}
 
 ApplicationRunnerChromium::~ApplicationRunnerChromium() {}
 
 void ApplicationRunnerChromium::set_message_loop_type(
     base::MessageLoop::Type type) {
-  DCHECK_EQ(base::MessageLoop::TYPE_DEFAULT, message_loop_type_);
+  DCHECK_NE(base::MessageLoop::TYPE_CUSTOM, type);
+  DCHECK(!has_run_);
+
   message_loop_type_ = type;
 }
 
 MojoResult ApplicationRunnerChromium::Run(MojoHandle shell_handle) {
+  DCHECK(!has_run_);
+  has_run_ = true;
+
   base::CommandLine::Init(0, NULL);
 #if !defined(COMPONENT_BUILD)
   base::AtExitManager at_exit;
 #endif
 
   {
-    base::MessageLoop loop(message_loop_type_);
+    scoped_ptr<base::MessageLoop> loop;
+    if (message_loop_type_ == base::MessageLoop::TYPE_CUSTOM) {
+      loop.reset(new base::MessageLoop(common::MessagePumpMojo::Create()));
+    } else {
+      loop.reset(new base::MessageLoop(message_loop_type_));
+    }
+
     ApplicationImpl impl(delegate_.get(),
                          MakeScopedHandle(MessagePipeHandle(shell_handle)));
-    loop.Run();
+    loop->Run();
   }
   delegate_.reset();
   return MOJO_RESULT_OK;
 }
 
 }  // namespace mojo