Revert "Allow SequencedTaskRunnerHandle::Get() while running unsequenced tasks."

base/threading/sequenced_task_runner_handle_unittest.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 "base/threading/sequenced_task_runner_handle.h"
 
 #include <memory>
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/location.h"
 #include "base/memory/ref_counted.h"
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/sequence_checker_impl.h"
 #include "base/sequenced_task_runner.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/test/sequenced_worker_pool_owner.h"
 #include "base/test/test_simple_task_runner.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "base/threading/simple_thread.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
 namespace {
 
 class SequencedTaskRunnerHandleTest : public ::testing::Test {
  protected:
+  // Verifies that the context it runs on has a SequencedTaskRunnerHandle
+  // and that posting to it results in the posted task running in that same
+  // context (sequence). Runs |callback| on sequence when done.
   static void VerifyCurrentSequencedTaskRunner(const Closure& callback) {
     ASSERT_TRUE(SequencedTaskRunnerHandle::IsSet());
     scoped_refptr<SequencedTaskRunner> task_runner =
         SequencedTaskRunnerHandle::Get();
     ASSERT_TRUE(task_runner);
 
     // Use SequenceCheckerImpl to make sure it's not a no-op in Release builds.
     std::unique_ptr<SequenceCheckerImpl> sequence_checker(
         new SequenceCheckerImpl);
     task_runner->PostTask(
         FROM_HERE,
         base::Bind(&SequencedTaskRunnerHandleTest::CheckValidSequence,
                    base::Passed(&sequence_checker), callback));
   }
 
+  // Verifies that there is no SequencedTaskRunnerHandle in the context it runs.
+  // Runs |callback| when done.
+  static void VerifyNoSequencedTaskRunner(const Closure& callback) {
+    ASSERT_FALSE(SequencedTaskRunnerHandle::IsSet());
+    callback.Run();
+  }
+
  private:
   static void CheckValidSequence(
       std::unique_ptr<SequenceCheckerImpl> sequence_checker,
       const Closure& callback) {
     EXPECT_TRUE(sequence_checker->CalledOnValidSequence());
     callback.Run();
   }
 
   MessageLoop message_loop_;
 };
 
 TEST_F(SequencedTaskRunnerHandleTest, FromMessageLoop) {
   RunLoop run_loop;
   VerifyCurrentSequencedTaskRunner(run_loop.QuitClosure());
   run_loop.Run();
 }
 
 TEST_F(SequencedTaskRunnerHandleTest, FromSequencedWorkerPoolTask) {
   // Wrap the SequencedWorkerPool to avoid leaks due to its asynchronous
   // destruction.
   SequencedWorkerPoolOwner owner(3, "Test");
   WaitableEvent event(WaitableEvent::ResetPolicy::AUTOMATIC,
                       WaitableEvent::InitialState::NOT_SIGNALED);
   owner.pool()->PostSequencedWorkerTask(
       owner.pool()->GetSequenceToken(), FROM_HERE,
       base::Bind(
           &SequencedTaskRunnerHandleTest::VerifyCurrentSequencedTaskRunner,
           base::Bind(&WaitableEvent::Signal, base::Unretained(&event))));
   event.Wait();
-  owner.pool()->Shutdown();
 }
 
-TEST_F(SequencedTaskRunnerHandleTest, FromUnsequencedTask) {
+TEST_F(SequencedTaskRunnerHandleTest, NoHandleFromUnsequencedTask) {
   // Wrap the SequencedWorkerPool to avoid leaks due to its asynchronous
   // destruction.
   SequencedWorkerPoolOwner owner(3, "Test");
   WaitableEvent event(WaitableEvent::ResetPolicy::AUTOMATIC,
                       WaitableEvent::InitialState::NOT_SIGNALED);
   owner.pool()->PostWorkerTask(
       FROM_HERE,
       base::Bind(
-          &SequencedTaskRunnerHandleTest::VerifyCurrentSequencedTaskRunner,
+          &SequencedTaskRunnerHandleTest::VerifyNoSequencedTaskRunner,
           base::Bind(&WaitableEvent::Signal, base::Unretained(&event))));
   event.Wait();
 }
 
 TEST(SequencedTaskRunnerHandleTestWithoutMessageLoop, FromHandleInScope) {
   scoped_refptr<SequencedTaskRunner> test_task_runner(new TestSimpleTaskRunner);
   EXPECT_FALSE(SequencedTaskRunnerHandle::IsSet());
   EXPECT_FALSE(ThreadTaskRunnerHandle::IsSet());
   {
     SequencedTaskRunnerHandle handle(test_task_runner);
     EXPECT_TRUE(SequencedTaskRunnerHandle::IsSet());
     EXPECT_FALSE(ThreadTaskRunnerHandle::IsSet());
     EXPECT_EQ(test_task_runner, SequencedTaskRunnerHandle::Get());
   }
   EXPECT_FALSE(SequencedTaskRunnerHandle::IsSet());
   EXPECT_FALSE(ThreadTaskRunnerHandle::IsSet());
 }
 
 }  // namespace
 }  // namespace base