Improve detection of compile-time errors.

pkg/front_end/lib/src/fasta/source/source_loader.dart

Index: pkg/front_end/lib/src/fasta/source/source_loader.dart
diff --git a/pkg/front_end/lib/src/fasta/source/source_loader.dart b/pkg/front_end/lib/src/fasta/source/source_loader.dart
index 3a5f82b14d84062be8a60f28fc0398f0de646c53..3c67c0cdc7668f6d4e23f360ac07fe28dd38faee 100644
--- a/pkg/front_end/lib/src/fasta/source/source_loader.dart
+++ b/pkg/front_end/lib/src/fasta/source/source_loader.dart
@@ -22,7 +22,7 @@ import 'package:kernel/class_hierarchy.dart' show ClassHierarchy;
 
 import 'package:kernel/core_types.dart' show CoreTypes;
 
-import '../errors.dart' show inputError, printUnexpected;
+import '../errors.dart' show inputError;
 
 import '../messages.dart' show warning;
 
@@ -75,7 +75,8 @@ class SourceLoader<L> extends Loader<L> {
       while (token is ErrorToken) {
         if (!suppressLexicalErrors) {
           ErrorToken error = token;
-          printUnexpected(uri, token.charOffset, error.assertionMessage);
+          library.addCompileTimeError(token.charOffset, error.assertionMessage,
+              fileUri: uri);
         }
         token = token.next;
       }