Correctly minify named mixin applications in dart2dart.

sdk/lib/_internal/compiler/implementation/dart_backend/placeholder_collector.dart

 // Copyright (c) 2012, 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.
 
 part of dart_backend;
 
 class LocalPlaceholder {
   final String identifier;
   final Set<Node> nodes;
   LocalPlaceholder(this.identifier) : nodes = new Set<Node>();
@@ skipping 561 matching lines @@
     if (node.defaultClause != null) {
       // Can't just visit class node's default clause because of the bug in the
       // resolver, it just crashes when it meets type variable.
       DartType defaultType = classElement.defaultClass;
       assert(defaultType != null);
       makeTypePlaceholder(node.defaultClause.typeName, defaultType);
       visit(node.defaultClause.typeArguments);
     }
   }
 
+  visitNamedMixinApplication(NamedMixinApplication node) {
+    ClassElement classElement = currentElement;
+    makeElementPlaceholder(node.name, classElement);
+    node.visitChildren(this);
+  }
+
   bool tryResolveAndCollectTypeVariable(
       TypeDeclarationElement typeDeclaration, Identifier name) {
     // Hack for case when interface and default class are in different
     // libraries, try to resolve type variable to default class type arg.
     // Example:
     // lib1: interface I<K> default C<K> {...}
     // lib2: class C<K> {...}
     if (typeDeclaration is ClassElement
         && (typeDeclaration as ClassElement).defaultClass != null) {
       typeDeclaration = (typeDeclaration as ClassElement).defaultClass.element;
@@ skipping 25 matching lines @@
 
   visitBlock(Block node) {
     for (Node statement in node.statements.nodes) {
       if (statement is VariableDefinitions) {
         makeVarDeclarationTypePlaceholder(statement);
       }
     }
     node.visitChildren(this);
   }
 }