base: Let ThreadTaskRunnerHandle::Get() return NULL

base/thread_task_runner_handle.cc

 // Copyright (c) 2012 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 "base/thread_task_runner_handle.h"
 
 #include "base/lazy_instance.h"
 #include "base/single_thread_task_runner.h"
 #include "base/threading/thread_local.h"
 
 namespace base {
 
 namespace {
 
 base::LazyInstance<base::ThreadLocalPointer<ThreadTaskRunnerHandle> >
     lazy_tls_ptr = LAZY_INSTANCE_INITIALIZER;
 
 }  // namespace
 
 // static
 scoped_refptr<SingleThreadTaskRunner> ThreadTaskRunnerHandle::Get() {
   ThreadTaskRunnerHandle* current = lazy_tls_ptr.Pointer()->Get();
-  DCHECK(current);
-  return current->task_runner_;
+  return current ? current->task_runner_ : nullptr;
 }
 
 // static
 bool ThreadTaskRunnerHandle::IsSet() {
   return lazy_tls_ptr.Pointer()->Get() != NULL;
 }
 
 ThreadTaskRunnerHandle::ThreadTaskRunnerHandle(
     const scoped_refptr<SingleThreadTaskRunner>& task_runner)
     : task_runner_(task_runner) {
   DCHECK(task_runner_->BelongsToCurrentThread());
   DCHECK(!lazy_tls_ptr.Pointer()->Get());
   lazy_tls_ptr.Pointer()->Set(this);
 }
 
 ThreadTaskRunnerHandle::~ThreadTaskRunnerHandle() {
   DCHECK(task_runner_->BelongsToCurrentThread());
   DCHECK_EQ(lazy_tls_ptr.Pointer()->Get(), this);
   lazy_tls_ptr.Pointer()->Set(NULL);
 }
 
 }  // namespace base