Flush InterfaceTypeImpl cached memebers when ClassElement.version is different.

pkg/analyzer/lib/src/task/incremental_element_builder.dart

 // Copyright (c) 2015, 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.task.incremental_element_builder;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
@@ skipping 316 matching lines @@
             parameterElement.field = newFields[parameterElement.name];
           }
         }
       }
     }
     // Update ClassElement.
     classElement.accessors = newAccessors;
     classElement.constructors = classElementHolder.constructors;
     classElement.fields = newFields.values.toList();
     classElement.methods = classElementHolder.methods;
+    classElement.version++;
     classElementHolder.validate();
     // Ensure at least a default synthetic constructor.
     if (classElement.constructors.isEmpty) {
       ConstructorElementImpl constructor =
           new ConstructorElementImpl.forNode(null);
       constructor.synthetic = true;
       classElement.constructors = <ConstructorElement>[constructor];
     }
     // OK
     return classDelta;
@@ skipping 347 matching lines @@
       }
     }
     super.visitElement(element);
   }
 
   static bool _isVariableInitializer(Element element) {
     return element is FunctionElement &&
         element.enclosingElement is VariableElement;
   }
 }