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

base/test/scoped_task_environment.cc

Index: base/test/scoped_task_environment.cc
diff --git a/base/test/scoped_task_environment.cc b/base/test/scoped_task_environment.cc
index af871e6a11d4c273197960d73ed3a1a227d32c86..d1c0907c4b0d7e32ab411826fe006c98efc3a7d6 100644
--- a/base/test/scoped_task_environment.cc
+++ b/base/test/scoped_task_environment.cc
@@ -12,6 +12,27 @@
 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
@@ -45,5 +66,19 @@ ScopedTaskEnvironment::~ScopedTaskEnvironment() {
   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