Keep cache entries for explicitly added sources.

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 547 matching lines @@
     // Stop depending on other results.
     TargetedResult thisResult = new TargetedResult(target, descriptor);
     for (TargetedResult dependedOnResult in thisData.dependedOnResults) {
       ResultData data = _partition._getDataFor(dependedOnResult);
       if (data != null && deltaResult != DeltaResult.KEEP_CONTINUE) {
         data.dependentResults.remove(thisResult);
       }
     }
     // Invalidate results that depend on this result.
     _invalidateDependentResults(id, thisData, delta, level + 1);
-    // If empty, remove the entry altogether.
-    if (_resultMap.isEmpty) {
+    // If empty and not explicitly added, remove the entry altogether.
+    if (_resultMap.isEmpty && !explicitlyAdded) {
       _partition._targetMap.remove(target);
       _partition._removeIfSource(target);
     }
     // Notify controller.
     _partition.onResultInvalidated
         .add(new InvalidatedResult(this, descriptor, thisData.value));
   }
 
   /**
    * Invalidates all the results of this entry, with propagation.
@@ skipping 646 matching lines @@
   void resultAccessed(TargetedResult result) {}
 
   @override
   List<TargetedResult> resultStored(TargetedResult newResult, newValue) {
     return TargetedResult.EMPTY_LIST;
   }
 
   @override
   void targetRemoved(AnalysisTarget target) {}
 }