When in strong mode, analyze with dart2js paths.

pkg/analyzer_cli/lib/src/driver.dart

Index: pkg/analyzer_cli/lib/src/driver.dart
diff --git a/pkg/analyzer_cli/lib/src/driver.dart b/pkg/analyzer_cli/lib/src/driver.dart
index a5d862e1ba092b20ee3321b6b7584ed1528c6d4f..cf570d49adb69ec08206e283f4416034cab8b4c8 100644
--- a/pkg/analyzer_cli/lib/src/driver.dart
+++ b/pkg/analyzer_cli/lib/src/driver.dart
@@ -617,8 +617,8 @@ class Driver implements CommandLineStarter {
             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;