Add base::test::ScopedTaskEnvironment::RunUntilIdle().

base/test/scoped_task_environment.cc

 // Copyright 2017 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_environment.h"
 
 #include "base/run_loop.h"
 #include "base/task_scheduler/scheduler_worker_pool_params.h"
 #include "base/task_scheduler/task_scheduler.h"
 #include "base/time/time.h"
 
 namespace base {
 namespace test {
 
+namespace {
+
+class TaskObserver : public MessageLoop::TaskObserver {
+ public:
+  TaskObserver() = default;
+
+  // MessageLoop::TaskObserver:
+  void WillProcessTask(const PendingTask& pending_task) override {}
+  void DidProcessTask(const PendingTask& pending_task) override {
+    ran_task_ = true;

[robliao, 2017/05/09 21:52:52]

It would be more accurate to call this called_did_process_task_. There's no task
associated with this observer.

+  }
+
+  bool ran_task() const { return ran_task_; }
+
+ private:
+  bool ran_task_ = false;
+  DISALLOW_COPY_AND_ASSIGN(TaskObserver);
+};
+
+}  // namespace
+
 ScopedTaskEnvironment::ScopedTaskEnvironment(MainThreadType main_thread_type)
     : message_loop_(main_thread_type == MainThreadType::DEFAULT
                         ? MessageLoop::TYPE_DEFAULT
                         : (main_thread_type == MainThreadType::UI
                                ? MessageLoop::TYPE_UI
                                : MessageLoop::TYPE_IO)) {
   DCHECK(!TaskScheduler::GetInstance());
 
   // Instantiate a TaskScheduler with 1 thread in each of its 4 pools. Threads
   // stay alive even when they don't have work.
@@ skipping 13 matching lines @@
 
   DCHECK_EQ(TaskScheduler::GetInstance(), task_scheduler_);
   // Without FlushForTesting(), DeleteSoon() and ReleaseSoon() tasks could be
   // skipped, resulting in memory leaks.
   TaskScheduler::GetInstance()->FlushForTesting();
   TaskScheduler::GetInstance()->Shutdown();
   TaskScheduler::GetInstance()->JoinForTesting();
   TaskScheduler::SetInstance(nullptr);
 }
 
+void ScopedTaskEnvironment::RunUntilIdle() {
+  for (;;) {
+    TaskScheduler::GetInstance()->FlushForTesting();
+
+    TaskObserver task_observer;
+    MessageLoop::current()->AddTaskObserver(&task_observer);
+    RunLoop().RunUntilIdle();
+    MessageLoop::current()->RemoveTaskObserver(&task_observer);
+
+    if (!task_observer.ran_task())
+      return;
+  }
+}
+
 }  // namespace test
 }  // namespace base