Run ScopedTaskScheduler tasks synchronously.

base/message_loop/message_loop.cc

 // Copyright 2013 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/message_loop/message_loop.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 339 matching lines @@
 std::string MessageLoop::GetThreadName() const {
   DCHECK_NE(kInvalidThreadId, thread_id_)
       << "GetThreadName() must only be called after BindToCurrentThread()'s "
       << "side-effects have been synchronized with this thread.";
   return ThreadIdNameManager::GetInstance()->GetName(thread_id_);
 }
 
 void MessageLoop::SetTaskRunner(
     scoped_refptr<SingleThreadTaskRunner> task_runner) {
   DCHECK_EQ(this, current());
-  DCHECK(task_runner->BelongsToCurrentThread());
+  DCHECK(!task_runner || task_runner->BelongsToCurrentThread());

[dcheng, 2016/12/15 06:47:36]

I would prefer we limit the API changes here to be available in tests only
(though I'm not sure if that's possible). Or are there other situations where
this would be useful?

[fdoray, 2016/12/15 16:39:31]

Done.

   DCHECK(!unbound_task_runner_);
   task_runner_ = std::move(task_runner);
   SetThreadTaskRunnerHandle();
 }
 
 void MessageLoop::SetThreadTaskRunnerHandle() {
   DCHECK_EQ(this, current());
   // Clear the previous thread task runner first, because only one can exist at
   // a time.
   thread_task_runner_handle_.reset();
-  thread_task_runner_handle_.reset(new ThreadTaskRunnerHandle(task_runner_));
+  if (task_runner_)
+    thread_task_runner_handle_.reset(new ThreadTaskRunnerHandle(task_runner_));
 }
 
 void MessageLoop::RunHandler() {
   DCHECK_EQ(this, current());
   DCHECK(run_loop_);
   CHECK(allow_nesting_ || run_loop_->run_depth_ == 1);
   pump_->Run(this);
 }
 
 bool MessageLoop::ProcessNextDelayedNonNestableTask() {
@@ skipping 272 matching lines @@
       persistent,
       mode,
       controller,
       delegate);
 }
 #endif
 
 #endif  // !defined(OS_NACL_SFI)
 
 }  // namespace base