Don't update incrementally invalid results.

pkg/analyzer/lib/src/context/cache.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.context.cache;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/engine.dart'
@@ skipping 491 matching lines @@
     if (_partition != null) {
       _partition.resultStored(thisResult, value);
     }
     ResultData data = getResultData(descriptor);
     _setDependedOnResults(data, thisResult, dependedOn);
     data.state = CacheState.VALID;
     data.value = value == null ? descriptor.defaultValue : value;
   }
 
   /**
-   * Set the value of the result represented by the given [descriptor] to the
-   * given [value], keep its dependency, invalidate all the dependent result.
+   * If the result represented by the given [descriptor] is valid, set
+   * it to the given [value], keep its dependency, and if [invalidateDependent]
+   * invalidate all the dependent result.
    */
   void setValueIncremental(
       ResultDescriptor descriptor, dynamic value, bool invalidateDependent) {
     ResultData data = getResultData(descriptor);
-    data.state = CacheState.VALID;
-    data.value = value;
+    if (data.state == CacheState.VALID) {

[Brian Wilkerson, 2015/11/20 19:47:47]

I think we want to also set the value if the state is FLUSHED.

+      data.value = value;
+    }
     if (invalidateDependent) {
       _invalidateDependentResults(nextInvalidateId++, data, null, 0);
     }
   }
 
   @override
   String toString() {
     StringBuffer buffer = new StringBuffer();
     _writeOn(buffer);
     return buffer.toString();
@@ skipping 731 matching lines @@
   void resultAccessed(TargetedResult result) {}
 
   @override
   List<TargetedResult> resultStored(TargetedResult newResult, newValue) {
     return TargetedResult.EMPTY_LIST;
   }
 
   @override
   void targetRemoved(AnalysisTarget target) {}
 }