Add Zone support for Timers.

sdk/lib/_internal/compiler/implementation/enqueue.dart

Index: sdk/lib/_internal/compiler/implementation/enqueue.dart
diff --git a/sdk/lib/_internal/compiler/implementation/enqueue.dart b/sdk/lib/_internal/compiler/implementation/enqueue.dart
index f3dae361521bf2bd7c029d6830d9e1249184ca28..1352ceaf87e01300c5033dbec7cc80964f4d660e 100644
--- a/sdk/lib/_internal/compiler/implementation/enqueue.dart
+++ b/sdk/lib/_internal/compiler/implementation/enqueue.dart
@@ -639,8 +639,8 @@ class ResolutionEnqueuer extends Enqueuer {
       if (uri == 'dart:isolate') {
         enableIsolateSupport(library);
       } else if (uri == 'dart:async') {
-        ClassElement cls = element.getEnclosingClass();
-        if (cls != null && cls.name == const SourceString('Timer')) {
+        if (element.name == const SourceString('_createTimer') ||
+            element.name == const SourceString('_createPeriodicTimer')) {
           // The [:Timer:] class uses the event queue of the isolate
           // library, so we make sure that event queue is generated.
           enableIsolateSupport(library);