[scheduler] Add options to TaskQueue::InsertFence

third_party/WebKit/Source/platform/scheduler/base/enqueue_order.h

Index: third_party/WebKit/Source/platform/scheduler/base/enqueue_order.h
diff --git a/third_party/WebKit/Source/platform/scheduler/base/enqueue_order.h b/third_party/WebKit/Source/platform/scheduler/base/enqueue_order.h
index 6b0e76bbdd83929adc6ced93e4ea6afa8eaea9ac..04932d54376478f53556d100ef23692280bee6ff 100644
--- a/third_party/WebKit/Source/platform/scheduler/base/enqueue_order.h
+++ b/third_party/WebKit/Source/platform/scheduler/base/enqueue_order.h
@@ -15,6 +15,16 @@ namespace internal {
 
 using EnqueueOrder = uint64_t;
 
+// TODO(scheduler-dev): Remove explicit casts when c++17 comes.
+enum class EnqueueOrderValues : EnqueueOrder {
+  // Invalid EnqueueOrder.
+  NONE = 0,
+
+  // Earliest possible EnqueueOrder, to be used for fence blocking.
+  BLOCKING_FENCE = 1,
+  FIRST = 2,
+};
+
 // A 64bit integer used to provide ordering of tasks. NOTE The scheduler assumes
 // these values will not overflow.
 class EnqueueOrderGenerator {