Use the saved task runner if TestTaskScheduler is re-entered from a task executed by RunTask.

base/test/scoped_task_scheduler_unittest.cc

 // Copyright 2016 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/test/scoped_task_scheduler.h"
 
 #include "base/bind.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/run_loop.h"
@@ skipping 278 matching lines @@
   PostDelayedTask(FROM_HERE, Bind(TestTaskRan, Unretained(&second_task_ran)),
                   TimeDelta());
 
   RunLoop().RunUntilIdle();
 
   // We never pumped |mock_time_task_runner| so the first task should not have
   // run.
   EXPECT_FALSE(first_task_ran);
   EXPECT_TRUE(second_task_ran);
 }
 

[fdoray, 2017/02/22 16:23:52]

// Verify that a task can be posted from a task running
// in ScopedTaskScheduler.

+TEST(ScopedTaskSchedulerTest, ReentrantTaskRunner) {
+  bool task_ran = false;
+  ScopedTaskScheduler scoped_task_scheduler;
+  PostTask(FROM_HERE, Bind(
+                          [](bool* task_ran) {
+                            PostTask(
+                                FROM_HERE,
+                                Bind([](bool* task_ran) { *task_ran = true; },
+                                     Unretained(task_ran)));
+                          },
+                          Unretained(&task_ran)));
+  RunLoop().RunUntilIdle();
+  EXPECT_TRUE(task_ran);
+}
+

[fdoray, 2017/02/22 16:23:52]

// Verify that ScopedTaskScheduler posts to the latest TaskRunner
// set on its MessageLoop, not the initial one.
TEST(ScopedTaskSchedulerTest, PostToCurrentMessageLoopTaskRunner) {
  bool task_ran = false;
  ScopedTaskScheduler scoped_task_scheduler;
  auto deferred_task_runner = make_scoped_ref_ptr(new
DeferredSequencedTaskRunner(base::ThreadTaskRunnerHandle::Get()));
  MessageLoop::current()->SetTaskRunner(deferred_task_runner);
  PostTask(
    FROM_HERE,
    Bind([] (bool* task_ran) { *task_ran = true; },
         Unretained(task_ran)));

  // The task shouldn't run if it was posted to
  // |deferred_task_runner| instead of the initial
  // MessageLoop's TaskRunner.
  RunLoop().RunUntilIdle();
  EXPECT_FALSE(task_ran);

  deferred_task_runner->Start();
  RunLoop().RunUntilIdle();
  EXPECT_TRUE(task_ran);     
}

[Joe Mason, 2017/02/22 20:23:30]

This test does the same thing as ReassignCurrentTaskRunner, except using
MessageLoop::SetTaskRunner directly instead of leveraging
ScopedMockTimeMessageLoopTaskRunner.

 }  // namespace test
 }  // namespace base