Do not duplicate constructors for named mixin applications.

lib/transformations/mixin_full_resolution.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 kernel.transformations.mixin_full_resolution;
 
 import '../ast.dart';
 import '../class_hierarchy.dart';
 import '../clone.dart';
 import '../core_types.dart';
 import '../type_algebra.dart';
@@ skipping 77 matching lines @@
     var substitution = getSubstitutionMap(class_.mixedInType);
     var cloner = new CloneVisitor(typeSubstitution: substitution);
     for (var field in class_.mixin.fields) {
       class_.addMember(cloner.clone(field));
     }
     for (var procedure in class_.mixin.procedures) {
       class_.addMember(cloner.clone(procedure));
     }
     // For each generative constructor in the superclass we make a
     // corresponding forwarding constructor in the subclass.
-    var superclassSubstitution = getSubstitutionMap(class_.supertype);
-    var superclassCloner =
-        new CloneVisitor(typeSubstitution: superclassSubstitution);
-    for (var superclassConstructor in class_.superclass.constructors) {
-      var forwardingConstructor =
-          buildForwardingConstructor(superclassCloner, superclassConstructor);
-      class_.constructors.add(forwardingConstructor..parent = class_);
+    // Named mixin applications already have constructors, so only build the
+    // constructors for anonymous mixin applications.
+    if (class_.constructors.isEmpty) {
+      var superclassSubstitution = getSubstitutionMap(class_.supertype);
+      var superclassCloner =
+          new CloneVisitor(typeSubstitution: superclassSubstitution);
+      for (var superclassConstructor in class_.superclass.constructors) {
+        var forwardingConstructor =
+            buildForwardingConstructor(superclassCloner, superclassConstructor);
+        class_.constructors.add(forwardingConstructor..parent = class_);
+      }
     }
 
     // This class implements the mixin type.
     class_.implementedTypes.add(class_.mixedInType);
 
     // This class is now a normal class.
     class_.mixedInType = null;
   }
 
   Constructor buildForwardingConstructor(
@@ skipping 240 matching lines @@
           return;
         }
       }
 
       throw new Exception(
           'Could not find a generative constructor named "${constructor.name}" '
           'in lookup class "${lookupClass.name}"!');
     }
   }
 }