Rewrite mixin application handling in Fasta.

pkg/front_end/lib/src/fasta/builder/builder.dart

Index: pkg/front_end/lib/src/fasta/builder/builder.dart
diff --git a/pkg/front_end/lib/src/fasta/builder/builder.dart b/pkg/front_end/lib/src/fasta/builder/builder.dart
index 90e4ffda163dedf0b03433c58fcbedca3c0be6ae..dffdfec22bc152b13af4e6f4124a10f48c9257df 100644
--- a/pkg/front_end/lib/src/fasta/builder/builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/builder.dart
@@ -24,8 +24,6 @@ export 'type_variable_builder.dart' show TypeVariableBuilder;
 
 export 'function_type_alias_builder.dart' show FunctionTypeAliasBuilder;
 
-export 'named_mixin_application_builder.dart' show NamedMixinApplicationBuilder;
-
 export 'mixin_application_builder.dart' show MixinApplicationBuilder;
 
 export 'enum_builder.dart' show EnumBuilder;
@@ -124,6 +122,8 @@ abstract class Builder {
 
   bool get isConst => false;
 
+  bool get isSynthetic => false;
+
   get target => internalError("Unsupported operation $runtimeType.");
 
   bool get hasProblem => false;