Add return value to RuntimeScheduler unstable_scheduleCallback

Summary:
Changelog: [internal]

unstable_scheduleCallback needs to return reference to the created task so it can be cancelled later.

Reviewed By: mdvacca

Differential Revision: D27622779

fbshipit-source-id: 54160015c7f98e123d08c2e13efac4f498d3ba5e

Author: sammy-SC

ReactCommon/react/renderer/runtimescheduler/RuntimeSchedulerBinding.cpp

@@ -7,6 +7,7 @@
 
 #include "RuntimeSchedulerBinding.h"
 #include "SchedulerPriority.h"
+#include "primitives.h"
 
 #include <react/debug/react_native_assert.h>
 #include <memory>
@@ -65,8 +66,7 @@ jsi::Value RuntimeSchedulerBinding::get(
           auto task = std::make_shared<Task>(priority, std::move(callback));
           runtimeScheduler_.scheduleTask(task);
 
-          // TODO: return reference to the task.
-          return jsi::Value::undefined();
+          return valueFromTask(runtime, task);
         });
   }
 

ReactCommon/react/renderer/runtimescheduler/primitives.h

@@ -0,0 +1,29 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+#include <folly/dynamic.h>
+#include <jsi/jsi.h>
+#include <react/renderer/runtimescheduler/Task.h>
+
+namespace facebook::react {
+
+struct TaskWrapper : public jsi::HostObject {
+  TaskWrapper(std::shared_ptr<Task> const &task) : task(task) {}
+
+  std::shared_ptr<Task> task;
+};
+
+inline static jsi::Value valueFromTask(
+    jsi::Runtime &runtime,
+    std::shared_ptr<Task> const &task) {
+  return jsi::Object::createFromHostObject(
+      runtime, std::make_shared<TaskWrapper>(task));
+}
+
+} // namespace facebook::react