Pass the 'strongMode' flag into SdkSummaryResynthesizer.

pkg/analyzer/lib/src/generated/sdk_io.dart

 // Copyright (c) 2014, 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.generated.sdk_io;
 
 import 'dart:collection';
 import 'dart:io';
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 266 matching lines @@
 
   @override
   AnalysisContext get context {
     if (_analysisContext == null) {
       _analysisContext = new SdkAnalysisContext(_analysisOptions);
       SourceFactory factory = new SourceFactory([new DartUriResolver(this)]);
       _analysisContext.sourceFactory = factory;
       if (_useSummary) {
         PackageBundle sdkBundle = getSummarySdkBundle();
         if (sdkBundle != null) {
-          _analysisContext.resultProvider =
-              new SdkSummaryResultProvider(_analysisContext, sdkBundle);
+          bool strongMode = _analysisOptions?.strongMode ?? false;
+          _analysisContext.resultProvider = new SdkSummaryResultProvider(
+              _analysisContext, sdkBundle, strongMode);
         }
       }
     }
     return _analysisContext;
   }
 
   /**
    * Return the file containing the dart2js executable, or `null` if it does not
    * exist.
    */
@@ skipping 384 matching lines @@
     SdkLibrariesReader_LibraryBuilder libraryBuilder =
         new SdkLibrariesReader_LibraryBuilder(_useDart2jsPaths);
     // If any syntactic errors were found then don't try to visit the AST
     // structure.
     if (!errorListener.errorReported) {
       unit.accept(libraryBuilder);
     }
     return libraryBuilder.librariesMap;
   }
 }