Clean up MojoShellConnection in render processes

mojo/shell/runner/host/out_of_process_native_runner.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/shell/runner/host/out_of_process_native_runner.h"
 
 #include <stdint.h>
 
 #include <utility>
 
@@ skipping 49 matching lines @@
 
 void OutOfProcessNativeRunner::AppCompleted(int32_t result) {
   DVLOG(2) << "OutOfProcessNativeRunner::AppCompleted(" << result << ")";
 
   if (child_process_host_)
     child_process_host_->Join();
   child_process_host_.reset();
   // This object may be deleted by this callback.
   base::Closure app_completed_callback = app_completed_callback_;
   app_completed_callback_.Reset();
-  app_completed_callback.Run();
+  if (!app_completed_callback.is_null())
+    app_completed_callback.Run();
 }
 
 void OutOfProcessNativeRunner::OnProcessLaunched(
     InterfaceRequest<mojom::ShellClient> request,
     const base::Callback<void(base::ProcessId)>& pid_available_callback,
     base::ProcessId pid) {
   DCHECK(child_process_host_);
   child_process_host_->StartApp(
       std::move(request),
       base::Bind(&OutOfProcessNativeRunner::AppCompleted,
                  base::Unretained(this)));
   pid_available_callback.Run(pid);
 }
 
 OutOfProcessNativeRunnerFactory::OutOfProcessNativeRunnerFactory(
     base::TaskRunner* launch_process_runner,
     NativeRunnerDelegate* delegate)
     : launch_process_runner_(launch_process_runner), delegate_(delegate) {}
 OutOfProcessNativeRunnerFactory::~OutOfProcessNativeRunnerFactory() {}
 
 scoped_ptr<shell::NativeRunner> OutOfProcessNativeRunnerFactory::Create(
     const base::FilePath& app_path) {
   return make_scoped_ptr(
       new OutOfProcessNativeRunner(launch_process_runner_, delegate_));
 }
 
 }  // namespace shell
 }  // namespace mojo