Extend the error framework to allow errors to have properties attached to them

editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/error/ErrorProperty.java

Index: editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/error/ErrorProperty.java
===================================================================
--- editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/error/ErrorProperty.java	(revision 0)
+++ editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/error/ErrorProperty.java	(revision 0)
@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2013, the Dart project authors.
+ * 
+ * Licensed under the Eclipse Public License v1.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ * 
+ * http://www.eclipse.org/legal/epl-v10.html
+ * 
+ * Unless required by applicable law or agreed to in writing, software distributed under the License
+ * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package com.google.dart.engine.error;
+
+/**
+ * The enumeration {@code ErrorProperty} defines the properties that can be associated with an
+ * {@link AnalysisError}.
+ */
+public enum ErrorProperty {
+  /**
+   * A property whose value is an array of {@link ExecutableElement executable elements} that should
+   * be but are not implemented by a concrete class.
+   */
+  UNIMPLEMENTED_METHODS;
+}