Add more CHECKs to help investigate the Mojo bootstrap crash

ipc/mojo/scoped_ipc_support.cc

 // Copyright 2015 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 "ipc/mojo/scoped_ipc_support.h"
 
 #include <stddef.h>
 
 #include "base/bind.h"
 #include "base/lazy_instance.h"
@@ skipping 67 matching lines @@
   // IO thread.
   MessageLoopObserver* observer_;
 
   scoped_refptr<base::TaskRunner> io_thread_task_runner_;
 
   DISALLOW_COPY_AND_ASSIGN(IPCSupportInitializer);
 };
 
 void IPCSupportInitializer::Init(
     scoped_refptr<base::TaskRunner> io_thread_task_runner) {
+  CHECK(io_thread_task_runner);
   base::AutoLock locker(lock_);
   DCHECK((init_count_ == 0 && !io_thread_task_runner_) ||
          io_thread_task_runner_ == io_thread_task_runner);
 
   if (shutting_down_) {
     // If reinitialized before a pending shutdown task is executed, we
     // effectively cancel the shutdown task.
     DCHECK(init_count_ == 1);
     shutting_down_ = false;
     return;
@@ skipping 60 matching lines @@
 ScopedIPCSupport::ScopedIPCSupport(
     scoped_refptr<base::TaskRunner> io_thread_task_runner) {
   ipc_support_initializer.Get().Init(io_thread_task_runner);
 }
 
 ScopedIPCSupport::~ScopedIPCSupport() {
   ipc_support_initializer.Get().ShutDown(false);
 }
 
 }  // namespace IPC