Stop precomputing ClassElement.isValidMixin.

pkg/analyzer/lib/src/dart/element/element.dart

 // Copyright (c) 2014, 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 analyzer.src.dart.element.element;
 
 import 'dart:collection';
 import 'dart:math' show min;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 318 matching lines @@
   bool get isProxy {
     for (ElementAnnotation annotation in metadata) {
       if (annotation.isProxy) {
         return true;
       }
     }
     return false;
   }
 
   @override
-  bool get isValidMixin => hasModifier(Modifier.MIXIN);
+  bool get isValidMixin {
+    if (!context.analysisOptions.enableSuperMixins) {
+      if (hasReferenceToSuper) {
+        return false;
+      }
+      if (!supertype.isObject) {
+        return false;
+      }
+    }
+    for (ConstructorElement constructor in constructors) {
+      if (!constructor.isSynthetic && !constructor.isFactory) {
+        return false;
+      }
+    }
+    return true;
+  }
 
   @override
   ElementKind get kind => ElementKind.CLASS;
 
   @override
   List<MethodElement> get methods => _methods;
 
   /**
    * Set the methods contained in this class to the given [methods].
    */
@@ skipping 29 matching lines @@
   ConstructorElement get unnamedConstructor {
     for (ConstructorElement element in constructors) {
       String name = element.displayName;
       if (name == null || name.isEmpty) {
         return element;
       }
     }
     return null;
   }
 
-  /**
-   * Set whether this class is a valid mixin.
-   */
-  void set validMixin(bool isValidMixin) {
-    setModifier(Modifier.MIXIN, isValidMixin);
-  }
-
   @override
   accept(ElementVisitor visitor) => visitor.visitClassElement(this);
 
   @override
   void appendTo(StringBuffer buffer) {
     if (isAbstract) {
       buffer.write('abstract ');
     }
     if (isEnum) {
       buffer.write('enum ');
@@ skipping 4192 matching lines @@
 
   @override
   void visitElement(Element element) {
     int offset = element.nameOffset;
     if (offset != -1) {
       map[offset] = element;
     }
     super.visitElement(element);
   }
 }