Dart2js async-await. Bind the async-body to the current zone.

pkg/compiler/lib/src/js_backend/backend.dart

Index: pkg/compiler/lib/src/js_backend/backend.dart
diff --git a/pkg/compiler/lib/src/js_backend/backend.dart b/pkg/compiler/lib/src/js_backend/backend.dart
index 3bc8c0f28a1957403ca1c30775e7036eedd30d82..2868e282dea6cf7331a5d7d6cd3f4daed8381850 100644
--- a/pkg/compiler/lib/src/js_backend/backend.dart
+++ b/pkg/compiler/lib/src/js_backend/backend.dart
@@ -1793,6 +1793,10 @@ class JavaScriptBackend extends Backend {
     return findHelper("asyncHelper");
   }
 
+  Element getWrapBody() {
+    return findHelper("_wrapJsFunctionForAsync");
+  }
+
   Element getYieldStar() {
     ClassElement classElement = findHelper("IterationMarker");
     classElement.ensureResolved(compiler);
@@ -2636,6 +2640,7 @@ class JavaScriptBackend extends Backend {
       enqueue(enqueuer, getAsyncHelper(), registry);
       enqueue(enqueuer, getCompleterConstructor(), registry);
       enqueue(enqueuer, getStreamIteratorConstructor(), registry);
+      enqueue(enqueuer, getWrapBody(), registry);
     } else if (element.asyncMarker == AsyncMarker.SYNC_STAR) {
       enqueuer.registerInstantiatedClass(getSyncStarIterable(), registry);
       enqueue(enqueuer, getSyncStarIterableConstructor(), registry);
@@ -2650,6 +2655,7 @@ class JavaScriptBackend extends Backend {
       enqueue(enqueuer, getYieldStar(), registry);
       enqueue(enqueuer, getASyncStarControllerConstructor(), registry);
       enqueue(enqueuer, getStreamIteratorConstructor(), registry);
+      enqueue(enqueuer, getWrapBody(), registry);
     }
   }
 }