Add a unit index to prelinked type references in summaries.

pkg/analyzer/lib/src/summary/summarize_elements.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 serialization.elements;
 
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/resolver.dart';
 import 'package:analyzer/src/generated/utilities_dart.dart';
 import 'package:analyzer/src/summary/builder.dart';
@@ skipping 537 matching lines @@
       if (dependentLibrary == null) {
         assert(type.isDynamic);
         if (type is UndefinedTypeImpl) {
           b.reference = serializeUnresolvedReference();
         } else {
           b.reference = serializeDynamicReference();
         }
       } else {
         b.reference = referenceMap.putIfAbsent(element, () {
           assert(unlinkedReferences.length == prelinkedReferences.length);
+          CompilationUnitElement unitElement =
+              element.getAncestor((Element e) => e is CompilationUnitElement);
+          int unit = dependentLibrary.units.indexOf(unitElement);
+          assert(unit != -1);
           int index = unlinkedReferences.length;
           // TODO(paulberry): set UnlinkedReference.prefix.
           unlinkedReferences
               .add(encodeUnlinkedReference(ctx, name: element.name));
           prelinkedReferences.add(encodePrelinkedReference(ctx,
               dependency: serializeDependency(dependentLibrary),
               kind: element is FunctionTypeAliasElement
                   ? PrelinkedReferenceKind.typedef
-                  : PrelinkedReferenceKind.classOrEnum));
+                  : PrelinkedReferenceKind.classOrEnum,
+              unit: unit));
           return index;
         });
       }
       List<DartType> typeArguments;
       if (type is InterfaceType) {
         typeArguments = type.typeArguments;
       } else if (type is FunctionType) {
         typeArguments = type.typeArguments;
       }
       if (typeArguments != null &&
@@ skipping 39 matching lines @@
     UnlinkedVariableBuilder b = new UnlinkedVariableBuilder(ctx);
     b.name = variable.name;
     b.unit = unitNum;
     b.type = serializeTypeRef(variable.type, variable);
     b.isStatic = variable.isStatic && variable.enclosingElement is ClassElement;
     b.isFinal = variable.isFinal;
     b.isConst = variable.isConst;
     return b;
   }
 }