step 1 in making unittest platform independent.

samples/tests/samples/src/dartcombat/DartCombatTest.dart

Index: samples/tests/samples/src/dartcombat/DartCombatTest.dart
diff --git a/samples/tests/samples/src/dartcombat/DartCombatTest.dart b/samples/tests/samples/src/dartcombat/DartCombatTest.dart
index 106980815e3c5dd03e032943a450e759d5d7c037..d50adcfb7a17e4e50d7dd8afb04c3565324f3edc 100644
--- a/samples/tests/samples/src/dartcombat/DartCombatTest.dart
+++ b/samples/tests/samples/src/dartcombat/DartCombatTest.dart
@@ -46,7 +46,7 @@ main() {
     // add a boat of length 4 using mousedown/mousemove/mouseup
     var startCell = p1OwnBoard.nodes[0].nodes[4].nodes[2];
     var endCell = p1OwnBoard.nodes[0].nodes[4].nodes[5];
-    serialInvokeAsync([
+    _serialInvokeAsync([
       () => doMouseEvent("mousedown", startCell),
       () => doMouseEvent("mousemove", endCell),
       () => doMouseEvent("mouseup", endCell),
@@ -82,7 +82,7 @@ main() {
     // add a boat of length 4 using mousedown/mousemove/mouseup
     var startCell = p2OwnBoard.nodes[0].nodes[3].nodes[8];
     var endCell = p2OwnBoard.nodes[0].nodes[7].nodes[8];
-    serialInvokeAsync([
+    _serialInvokeAsync([
       () => doMouseEvent("mousedown", startCell),
       () => doMouseEvent("mousemove", endCell),
       () => doMouseEvent("mouseup", endCell),
@@ -148,3 +148,18 @@ doMouseEvent(String type, var targetCell) {
       relatedTarget: targetCell);
   targetCell.on[type].dispatch(e);
 }
+
+void _serialInvokeAsync(List closures) {
+  final length = closures.length;
+  if (length > 0) {
+    int i = 0;
+    void invokeNext() {
+      closures[i]();
+      i++;
+      if (i < length) {
+        window.setTimeout(invokeNext, 0);
+      }
+    }
+    window.setTimeout(invokeNext, 0);
+  }
+}