Use artificial hashCode values.

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

Index: pkg/analyzer/lib/src/task/model.dart
diff --git a/pkg/analyzer/lib/src/task/model.dart b/pkg/analyzer/lib/src/task/model.dart
index a48f85a983b84d1a74bdcb9394549ee58a013353..9ef568e5c1ef7cba89d9da8ef68e8d14ba3f74cf 100644
--- a/pkg/analyzer/lib/src/task/model.dart
+++ b/pkg/analyzer/lib/src/task/model.dart
@@ -37,6 +37,11 @@ class ListResultDescriptorImpl<E> extends ResultDescriptorImpl<List<E>>
  * A concrete implementation of a [ResultDescriptor].
  */
 class ResultDescriptorImpl<V> implements ResultDescriptor<V> {
+  static int _NEXT_HASH = 0;
+
+  @override
+  final hashCode = _NEXT_HASH++;
+
   /**
    * The name of the result, used for debugging.
    */
@@ -61,6 +66,11 @@ class ResultDescriptorImpl<V> implements ResultDescriptor<V> {
       {this.cachingPolicy: DEFAULT_CACHING_POLICY});
 
   @override
+  bool operator ==(Object other) {
+    return other is ResultDescriptorImpl && other.hashCode == hashCode;
+  }
+
+  @override
   TaskInput<V> of(AnalysisTarget target) =>
       new SimpleTaskInput<V>(target, this);