Support SequencedWorkerPool::FlushForTesting() with redirection to TaskScheduler.

base/threading/sequenced_worker_pool.cc

Index: base/threading/sequenced_worker_pool.cc
diff --git a/base/threading/sequenced_worker_pool.cc b/base/threading/sequenced_worker_pool.cc
index 01f3329599fce0e3e077e4c1995222a997045054..acc7e50633e163e2730e5f25d1224665f5731340 100644
--- a/base/threading/sequenced_worker_pool.cc
+++ b/base/threading/sequenced_worker_pool.cc
@@ -895,8 +895,6 @@ bool SequencedWorkerPool::Inner::IsRunningSequenceOnCurrentThread(
 void SequencedWorkerPool::Inner::CleanupForTesting() {
   DCHECK_NE(subtle::NoBarrier_Load(&g_all_pools_state),
             AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER);
-  DCHECK(!RunsTasksOnCurrentThread());
-  base::ThreadRestrictions::ScopedAllowWait allow_wait;
   AutoLock lock(lock_);
   CHECK_EQ(CLEANUP_DONE, cleanup_state_);
   if (shutdown_called_)
@@ -1598,7 +1596,15 @@ bool SequencedWorkerPool::RunsTasksOnCurrentThread() const {
 }
 
 void SequencedWorkerPool::FlushForTesting() {
-  inner_->CleanupForTesting();
+  DCHECK(!RunsTasksOnCurrentThread());
+  base::ThreadRestrictions::ScopedAllowWait allow_wait;
+  if (subtle::NoBarrier_Load(&g_all_pools_state) ==
+      AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER) {
+    // TODO(gab): Remove this if http://crbug.com/622400 fails.
+    TaskScheduler::GetInstance()->FlushForTesting();
+  } else {
+    inner_->CleanupForTesting();
+  }
 }
 
 void SequencedWorkerPool::SignalHasWorkForTesting() {