When in strong mode, analyze with dart2js paths.

pkg/analyzer_cli/lib/src/driver.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_cli.src.driver;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
@@ skipping 599 matching lines @@
     return errorSeverity;
   }
 
   void _setupSdk(CommandLineOptions options, bool hasEmbedder) {
     if (sdk == null) {
       if (options.dartSdkSummaryPath != null) {
         sdk = new SummaryBasedDartSdk(
             options.dartSdkSummaryPath, options.strongMode);
       } else {
         String dartSdkPath = options.dartSdkPath;
-        DirectoryBasedDartSdk directorySdk =
-            new DirectoryBasedDartSdk(new JavaFile(dartSdkPath));
+        DirectoryBasedDartSdk directorySdk = new DirectoryBasedDartSdk(
+            new JavaFile(dartSdkPath), options.strongMode);
         // Summaries are disabled in the presence of embedders.
         if (hasEmbedder) {
           directorySdk.useSummary = false;
         } else {
           directorySdk.useSummary =
               options.sourceFiles.every((String sourcePath) {
             sourcePath = path.absolute(sourcePath);
             sourcePath = path.normalize(sourcePath);
             return !path.isWithin(dartSdkPath, sourcePath);
           });
@@ skipping 198 matching lines @@
     for (var package in packages) {
       var packageName = path.basename(package.path);
       var realPath = package.resolveSymbolicLinksSync();
       result[packageName] = [
         PhysicalResourceProvider.INSTANCE.getFolder(realPath)
       ];
     }
     return result;
   }
 }