Add more mixin tests and start rejecting illegal syntax.

sdk/lib/_internal/compiler/implementation/scanner/listener.dart

Index: sdk/lib/_internal/compiler/implementation/scanner/listener.dart
diff --git a/sdk/lib/_internal/compiler/implementation/scanner/listener.dart b/sdk/lib/_internal/compiler/implementation/scanner/listener.dart
index dd979a1c0c3c2d5e4c769f14a3572397c53c7dbd..8f1b67529b608fda54b9c3e51ffc616e7e6b71ca 100644
--- a/sdk/lib/_internal/compiler/implementation/scanner/listener.dart
+++ b/sdk/lib/_internal/compiler/implementation/scanner/listener.dart
@@ -835,8 +835,9 @@ class ElementListener extends Listener {
 
     int id = idGenerator();
     Element enclosing = compilationUnitElement;
-    pushElement(new MixinApplicationElementX(
-        name.source, enclosing, id, namedMixinApplication));
+    pushElement(new MixinApplicationElementX(name.source, enclosing, id,
+                                             namedMixinApplication,
+                                             mixinApplication.modifiers));
     rejectBuiltInIdentifier(name);
   }