Rewrite mixin application handling in Fasta.

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

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library fasta.named_type_builder;
 
 import 'builder.dart'
     show
         Builder,
         InvalidTypeBuilder,
@@ skipping 12 matching lines @@
   NamedTypeBuilder(this.name, this.arguments, int charOffset, Uri fileUri)
       : super(charOffset, fileUri);
 
   InvalidTypeBuilder<T, R> buildInvalidType(String name);
 
   void bind(TypeDeclarationBuilder builder) {
     this.builder = builder;
   }
 
   void resolveIn(Scope scope) {
+    if (builder != null) return;
     Builder member = scope.lookup(name, charOffset, fileUri);
     if (member is TypeDeclarationBuilder) {
       builder = member;
       return;
     }
     if (name.contains(".")) {
       int index = name.lastIndexOf(".");
       String first = name.substring(0, index);
       String last = name.substring(name.lastIndexOf(".") + 1);
       var prefix = scope.lookup(first, charOffset, fileUri);
       if (prefix is PrefixBuilder) {
         member = prefix.lookup(last, charOffset, fileUri);
       }
       if (member is TypeDeclarationBuilder) {
         builder = member;
         return;
       }
     }
     builder = buildInvalidType(name);
   }
 
   String get debugName => "NamedTypeBuilder";
 
   StringBuffer printOn(StringBuffer buffer) {
     buffer.write(name);
-    if (arguments == null) return buffer;
+    if (arguments?.isEmpty ?? true) return buffer;
     buffer.write("<");
     bool first = true;
     for (T t in arguments) {
       if (!first) buffer.write(", ");
       first = false;
       t.printOn(buffer);
     }
     buffer.write(">");
     return buffer;
   }
 }