Use MockSdk.getLinkedBundle(), and implement it using SummaryBuilder.

pkg/analyzer/test/src/context/mock_sdk.dart

Index: pkg/analyzer/test/src/context/mock_sdk.dart
diff --git a/pkg/analyzer/test/src/context/mock_sdk.dart b/pkg/analyzer/test/src/context/mock_sdk.dart
index e0a9575c1f5e82d173d6a2768cbdce71fb0e1443..91b4e5e5b0376758575ad918a7a72ca8b9712d48 100644
--- a/pkg/analyzer/test/src/context/mock_sdk.dart
+++ b/pkg/analyzer/test/src/context/mock_sdk.dart
@@ -4,7 +4,6 @@
 
 library analyzer.test.src.context.mock_sdk;
 
-import 'package:analyzer/dart/element/element.dart' show LibraryElement;
 import 'package:analyzer/file_system/file_system.dart' as resource;
 import 'package:analyzer/file_system/memory_file_system.dart' as resource;
 import 'package:analyzer/src/context/cache.dart';
@@ -13,8 +12,7 @@ import 'package:analyzer/src/generated/engine.dart' show AnalysisEngine;
 import 'package:analyzer/src/generated/sdk.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/summary/idl.dart' show PackageBundle;
-import 'package:analyzer/src/summary/summarize_elements.dart'
-    show PackageBundleAssembler;
+import 'package:analyzer/src/summary/summary_file_builder.dart';
 
 const String librariesContent = r'''
 const Map<String, LibraryInfo> libraries = const {
@@ -407,14 +405,12 @@ class MockSdk implements DartSdk {
   @override
   PackageBundle getLinkedBundle() {
     if (_bundle == null) {
-      PackageBundleAssembler assembler = new PackageBundleAssembler();
-      for (SdkLibrary sdkLibrary in sdkLibraries) {
-        String uriStr = sdkLibrary.shortName;
-        Source source = mapDartUri(uriStr);
-        LibraryElement libraryElement = context.computeLibraryElement(source);
-        assembler.serializeLibraryElement(libraryElement);
-      }
-      List<int> bytes = assembler.assemble().toBuffer();
+      List<Source> librarySources = sdkLibraries
+          .map((SdkLibrary library) => mapDartUri(library.shortName))
+          .toList();
+      List<int> bytes = new SummaryBuilder(
+              librarySources, context, context.analysisOptions.strongMode)
+          .build();
       _bundle = new PackageBundle.fromBuffer(bytes);
     }
     return _bundle;