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

base/test/scoped_task_environment.h

Index: base/test/scoped_task_environment.h
diff --git a/base/test/scoped_task_environment.h b/base/test/scoped_task_environment.h
index 04b9c75b1bf10ff3b5c8df2b4cbcbe950f92fd30..7b7180ae83292b2ed67b47c906f4a8b257637b31 100644
--- a/base/test/scoped_task_environment.h
+++ b/base/test/scoped_task_environment.h
@@ -22,12 +22,14 @@ namespace test {
 // ScopedTaskEnvironment.
 //
 // Tasks posted to the (Thread|Sequenced)TaskRunnerHandle run synchronously when
-// RunLoop::Run(UntilIdle) is called on the thread where the
-// ScopedTaskEnvironment lives.
+// RunLoop::Run(UntilIdle) or ScopedTaskEnvironment::RunUntilIdle is called on

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

Nit: RunUntilIdle()

+// the thread where the ScopedTaskEnvironment lives.
 //
 // Tasks posted through base/task_scheduler/post_task.h run on dedicated threads
 // as they are posted.
 //
+// All methods of ScopedTaskEnvironment must be called from the same thread.
+//
 // Usage:
 //
 //   class MyTestFixture : public testing::Test {
@@ -66,6 +68,10 @@ class ScopedTaskEnvironment {
   // the (Thread|Sequenced)TaskRunnerHandle.
   ~ScopedTaskEnvironment();
 
+  // Synchronously runs (Thread|Sequenced)TaskRunnerHandle tasks until no
+  // undelayed (Thread|Sequenced)TaskRunnerHandle or TaskScheduler tasks remain.
+  void RunUntilIdle();
+
  private:
   // Note: |message_loop_| is an implementation detail and will be replaced in
   // the future, do NOT rely on the presence of a MessageLoop beyond