Add ScopedTaskEnvironment::ExecutionControlMode.

base/task_scheduler/task_scheduler_impl.h

Index: base/task_scheduler/task_scheduler_impl.h
diff --git a/base/task_scheduler/task_scheduler_impl.h b/base/task_scheduler/task_scheduler_impl.h
index 4907ce2df266e91e6aac6de9df4f213a1fa419dd..69d70f00635169d3016ee047a461ca87896f9638 100644
--- a/base/task_scheduler/task_scheduler_impl.h
+++ b/base/task_scheduler/task_scheduler_impl.h
@@ -12,6 +12,7 @@
 #include "base/callback.h"
 #include "base/logging.h"
 #include "base/macros.h"
+#include "base/memory/ptr_util.h"
 #include "base/memory/ref_counted.h"
 #include "base/strings/string_piece.h"
 #include "base/synchronization/atomic_flag.h"
@@ -38,8 +39,17 @@ namespace internal {
 // Default TaskScheduler implementation. This class is thread-safe.
 class BASE_EXPORT TaskSchedulerImpl : public TaskScheduler {
  public:
+  using TaskTrackerType =
+#if defined(OS_POSIX) && !defined(OS_NACL_SFI)
+      TaskTrackerPosix;
+#else
+      TaskTracker;
+#endif
+
   // |name| is used to label threads and histograms.

[robliao, 2017/05/19 20:14:47]

Comment on |task_tracker|.
|task_tracker| can be used for tests that need more execution control. By
default, you get the production task tracker.

[fdoray, 2017/05/23 14:04:48]

Done.

-  explicit TaskSchedulerImpl(StringPiece name);
+  explicit TaskSchedulerImpl(StringPiece name,
+                             std::unique_ptr<TaskTrackerType> task_tracker =
+                                 MakeUnique<TaskTrackerType>());
   ~TaskSchedulerImpl() override;
 
   // TaskScheduler:
@@ -74,11 +84,7 @@ class BASE_EXPORT TaskSchedulerImpl : public TaskScheduler {
 
   const std::string name_;
   Thread service_thread_;
-#if defined(OS_POSIX) && !defined(OS_NACL_SFI)
-  TaskTrackerPosix task_tracker_;
-#else
-  TaskTracker task_tracker_;
-#endif
+  const std::unique_ptr<TaskTrackerType> task_tracker_;
   DelayedTaskManager delayed_task_manager_;
   SchedulerSingleThreadTaskRunnerManager single_thread_task_runner_manager_;