Add support for Scheduler#postTask

Author: armanbilge

core/src/main/scala/org/scalajs/macrotaskexecutor/MacrotaskExecutor.scala

@@ -35,7 +35,19 @@ object MacrotaskExecutor extends ExecutionContextExecutor {
     cause.printStackTrace()
 
   private[this] val setImmediate: (() => Unit) => Unit = {
-    if (js.typeOf(js.Dynamic.global.setImmediate) == Undefined) {
+    if (js.typeOf(js.Dynamic.global.setImmediate) != Undefined) {
+      { k =>
+        js.Dynamic.global.setImmediate(k)
+        ()
+      }
+    } else if (js.typeOf(js.Dynamic.global.scheduler) != Undefined
+                && js.typeOf(js.Dynamic.global.scheduler.postTask) != Undefined) {
+      { k =>
+        js.Dynamic.global.scheduler.postTask(k)
+        ()
+      }
+    } else {
+      
       var nextHandle = 1
       val tasksByHandle = mutable.Map[Int, () => Unit]()
       var currentlyRunningATask = false
@@ -157,11 +169,6 @@ object MacrotaskExecutor extends ExecutionContextExecutor {
           ()
         }
       }
-    } else {
-      { k =>
-        js.Dynamic.global.setImmediate(k)
-        ()
-      }
     }
   }