Use j.u.HashMap instead of Scala Map

Author: armanbilge

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

@@ -16,7 +16,7 @@
 
 package org.scalajs.macrotaskexecutor
 
-import scala.collection.mutable
+import java.util.HashMap
 import scala.concurrent.{ExecutionContext, ExecutionContextExecutor}
 import scala.scalajs.js
 import scala.util.Random
@@ -37,7 +37,7 @@ object MacrotaskExecutor extends ExecutionContextExecutor {
   private[this] val setImmediate: Runnable => Unit = {
     if (js.typeOf(js.Dynamic.global.setImmediate) == Undefined) {
       var nextHandle = 1
-      val tasksByHandle = mutable.Map[Int, Runnable]()
+      val tasksByHandle = new HashMap[Int, Runnable]
       var currentlyRunningATask = false
 
       def canUsePostMessage(): Boolean = {
@@ -67,17 +67,15 @@ object MacrotaskExecutor extends ExecutionContextExecutor {
         if (currentlyRunningATask) {
           js.Dynamic.global.setTimeout(() => runIfPresent(handle), 0)
         } else {
-          tasksByHandle.get(handle) match {
-            case Some(task) =>
-              currentlyRunningATask = true
-              try {
-                task.run()
-              } finally {
-                tasksByHandle -= handle
-                currentlyRunningATask = false
-              }
-
-            case None =>
+          val task = tasksByHandle.get(handle)
+          if (task ne null) {
+            currentlyRunningATask = true
+            try {
+              task.run()
+            } finally {
+              tasksByHandle -= handle
+              currentlyRunningATask = false
+            }
           }
         }