Fix issues from CL 3009573002.

pkg/front_end/lib/src/fasta/kernel/kernel_target.dart

Index: pkg/front_end/lib/src/fasta/kernel/kernel_target.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_target.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_target.dart
index c1c52c78c491f81269b9a35226db0c67530af74b..3c78012ac85b3126866cd6efd2fb6aab457f4941 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_target.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_target.dart
@@ -371,7 +371,7 @@ class KernelTarget extends TargetImplementation {
         nameRoot: nameRoot, libraries: libraries, uriToSource: uriToSource);
     if (loader.first != null) {
       // TODO(sigmund): do only for full program
-      Builder builder = loader.first.lookup("main", -1, null);
+      Builder builder = loader.first.exportScope.lookup("main", -1, null);
       if (builder is KernelProcedureBuilder) {
         program.mainMethod = builder.procedure;
       }