Fix async_test problems.

pkg/compiler/lib/src/resolution/members.dart

Index: pkg/compiler/lib/src/resolution/members.dart
diff --git a/pkg/compiler/lib/src/resolution/members.dart b/pkg/compiler/lib/src/resolution/members.dart
index 2611192b7ca9cffb378e6c9a833af41840c70e13..206a0352c1e3744345e64ba74f62ea0268cc5a44 100644
--- a/pkg/compiler/lib/src/resolution/members.dart
+++ b/pkg/compiler/lib/src/resolution/members.dart
@@ -516,11 +516,19 @@ class ResolverTask extends CompilerTask {
         compiler.reportError(asyncModifier,
             MessageKind.ASYNC_MODIFIER_ON_CONSTRUCTOR,
             {'modifier': element.asyncMarker});
-      } else if (functionExpression.body.asReturn() != null &&
+      } else {
+        if (element.isSetter) {
+          compiler.reportError(asyncModifier,
+              MessageKind.ASYNC_MODIFIER_ON_SETTER,
+              {'modifier': element.asyncMarker});
+
+        }
+        if (functionExpression.body.asReturn() != null &&
                  element.asyncMarker.isYielding) {
-        compiler.reportError(asyncModifier,
-            MessageKind.YIELDING_MODIFIER_ON_ARROW_BODY,
-            {'modifier': element.asyncMarker});
+          compiler.reportError(asyncModifier,
+              MessageKind.YIELDING_MODIFIER_ON_ARROW_BODY,
+              {'modifier': element.asyncMarker});
+        }
       }
     }
   }