Anonymous mixin applications are abstract

Change-Id: Ib36a0bd243010a5b51bf49bda750d7e432017eae
Reviewed-on: https://dart-review.googlesource.com/c/90703
Commit-Queue: Peter von der Ahé <ahe@google.com>
Reviewed-by: Jenny Messerly <jmesserly@google.com>
diff --git a/pkg/dev_compiler/lib/src/kernel/analyzer_to_kernel.dart b/pkg/dev_compiler/lib/src/kernel/analyzer_to_kernel.dart
index 5c91caa..917daa3 100644
--- a/pkg/dev_compiler/lib/src/kernel/analyzer_to_kernel.dart
+++ b/pkg/dev_compiler/lib/src/kernel/analyzer_to_kernel.dart
@@ -311,7 +311,7 @@
 
       var c = Class(
           name: runningName,
-          isAbstract: e.isAbstract,
+          isAbstract: true,
           mixedInType: mixedInType,
           supertype: supertype,
           typeParameters: typeParameters,