Fix reference sharing in the event that import prefixes are used.

pkg/analyzer/lib/src/summary/link.dart

 // Copyright (c) 2016, 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.
 
 /**
  * This library is capable of producing linked summaries from unlinked
  * ones (or prelinked ones).  It functions by building a miniature
  * element model to represent the contents of the summaries, and then
  * scanning the element model to gather linked information and adding
  * it to the summary data structures.
@@ skipping 1061 matching lines @@
   int addRawReference(String name,
       {int dependency: 0,
       int numTypeParameters: 0,
       int unitNum: 0,
       int containingReference: 0,
       ReferenceKind kind: ReferenceKind.classOrEnum}) {
     List<LinkedReferenceBuilder> linkedReferences = _linkedUnit.references;
     List<UnlinkedReference> unlinkedReferences = _unlinkedUnit.references;
     for (int i = 0; i < linkedReferences.length; i++) {
       LinkedReferenceBuilder linkedReference = linkedReferences[i];
+      int candidateContainingReference = i < unlinkedReferences.length
+          ? unlinkedReferences[i].prefixReference
+          : linkedReference.containingReference;
+      if (candidateContainingReference != 0 &&
+          linkedReferences[candidateContainingReference].kind ==
+              ReferenceKind.prefix) {
+        // We don't need to match containing references when they are prefixes,
+        // since the relevant information is in linkedReference.dependency.
+        candidateContainingReference = 0;
+      }
       if (linkedReference.dependency == dependency &&
           (i < unlinkedReferences.length
                   ? unlinkedReferences[i].name
                   : linkedReference.name) ==
               name &&
           linkedReference.numTypeParameters == numTypeParameters &&
           linkedReference.unit == unitNum &&
-          (i < unlinkedReferences.length
-                  ? unlinkedReferences[i].prefixReference
-                  : linkedReference.containingReference) ==
-              containingReference &&
+          candidateContainingReference == containingReference &&
           linkedReference.kind == kind) {
         return i;
       }
     }
     int result = linkedReferences.length;
     linkedReferences.add(new LinkedReferenceBuilder(
         dependency: dependency,
         name: name,
         numTypeParameters: numTypeParameters,
         unit: unitNum,
@@ skipping 3627 matching lines @@
    * there are no type parameters in scope.
    */
   TypeParameterizedElementForLink get _typeParameterContext;
 
   @override
   noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
 
   @override
   String toString() => '$enclosingElement.$name';
 }