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());
   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_)

[robliao, 2016/12/09 01:32:54]

Should we DCHECK here? Seems unexpected to silently reset and not set a
ThreadTaskRunnerHandle, even if there is no valid task_runner_ available.

[fdoray, 2016/12/09 16:26:41]

It is intentional to have no ThreadTaskRunnerHandle on the current thread after
calling SetThreadTaskRunnerHandle() with |task_runner_| == nullptr. This is what
allows the ScopedTaskScheduler's TaskTracker to set its own
Thread/SequencedTaskRunnerHandle.

+    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