Add ScopedTaskEnvironment::ExecutionControlMode.

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 f46b516d7c16ddea6d7a6b710fd9a7832045dc29..5166a5e776c790d03585f8afd56847d186962983 100644
--- a/base/test/scoped_task_environment.h
+++ b/base/test/scoped_task_environment.h
@@ -26,7 +26,9 @@ namespace test {
 // RunLoop::Run(UntilIdle) or ScopedTaskEnvironment::RunUntilIdle is called on
 // the thread where the ScopedTaskEnvironment lives.
 //
-// Tasks posted through base/task_scheduler/post_task.h run on dedicated threads
+// Tasks posted through base/task_scheduler/post_task.h run on dedicated
+// threads. If ExecutionMode is QUEUED, they run when RunUntilIdle() or
+// ~ScopedTaskEnvironment is called. If ExecutionMode is ASYNC, they run
 // as they are posted.
 //
 // All methods of ScopedTaskEnvironment must be called from the same thread.
@@ -61,8 +63,18 @@ class ScopedTaskEnvironment {
     IO,
   };
 
+  enum class ExecutionMode {
+    // Tasks are queued and only executed when RunUntilIdle() is explicitly
+    // called.
+    QUEUED,
+    // Tasks run as they are posted. RunUntilIdle() can still be used to block
+    // until done.
+    ASYNC,
+  };
+
   ScopedTaskEnvironment(
-      MainThreadType main_thread_type = MainThreadType::DEFAULT);
+      MainThreadType main_thread_type = MainThreadType::DEFAULT,
+      ExecutionMode execution_control_mode = ExecutionMode::ASYNC);
 
   // Waits until no undelayed TaskScheduler tasks remain. Then, unregisters the
   // TaskScheduler and the (Thread|Sequenced)TaskRunnerHandle.
@@ -71,11 +83,15 @@ class ScopedTaskEnvironment {
   // Returns a TaskRunner that schedules tasks on the main thread.
   scoped_refptr<base::SingleThreadTaskRunner> GetMainThreadTaskRunner();
 
-  // Synchronously runs (Thread|Sequenced)TaskRunnerHandle tasks until no
-  // undelayed (Thread|Sequenced)TaskRunnerHandle or TaskScheduler tasks remain.
+  // Runs tasks until both the (Thread|Sequenced)TaskRunnerHandle and the
+  // TaskScheduler queues are empty.
   void RunUntilIdle();
 
  private:
+  class TestTaskTracker;
+
+  const ExecutionMode execution_control_mode_;
+
   // Note: |message_loop_| is an implementation detail and will be replaced in
   // the future, do NOT rely on the presence of a MessageLoop beyond
   // (Thread|Sequenced)TaskRunnerHandle and RunLoop.
@@ -83,6 +99,9 @@ class ScopedTaskEnvironment {
 
   const TaskScheduler* task_scheduler_ = nullptr;
 
+  // Owned by |task_scheduler_|.
+  TestTaskTracker* const task_tracker_;
+
   DISALLOW_COPY_AND_ASSIGN(ScopedTaskEnvironment);
 };