Use FastaMessage instead of String. Part 1.

pkg/front_end/lib/src/fasta/loader.dart

Index: pkg/front_end/lib/src/fasta/loader.dart
diff --git a/pkg/front_end/lib/src/fasta/loader.dart b/pkg/front_end/lib/src/fasta/loader.dart
index ed576aa07c5b9977983fb3177cbb1cf1e727e294..273f1a50312a33b6f3d3fa50fe64513a1e04ab00 100644
--- a/pkg/front_end/lib/src/fasta/loader.dart
+++ b/pkg/front_end/lib/src/fasta/loader.dart
@@ -11,7 +11,9 @@ import 'dart:collection' show Queue;
 import 'builder/builder.dart' show Builder, LibraryBuilder;
 
 import 'deprecated_problems.dart'
-    show deprecated_InputError, firstSourceUri, deprecated_printUnexpected;
+    show firstSourceUri, deprecated_printUnexpected;
+
+import 'messages.dart' show LocatedMessage, Message, templateUnspecified;
 
 import 'target_implementation.dart' show TargetImplementation;
 
@@ -31,14 +33,14 @@ abstract class Loader<L> {
   ///
   /// A handled error is an error that has been added to the generated AST
   /// already, for example, as a throw expression.
-  final List<deprecated_InputError> handledErrors = <deprecated_InputError>[];
+  final List<LocatedMessage> handledErrors = <LocatedMessage>[];
 
   /// List of all unhandled compile-time errors seen so far by libraries loaded
   /// by this loader.
   ///
   /// An unhandled error is an error that hasn't been handled, see
   /// [handledErrors].
-  final List<deprecated_InputError> unhandledErrors = <deprecated_InputError>[];
+  final List<LocatedMessage> unhandledErrors = <LocatedMessage>[];
 
   LibraryBuilder coreLibrary;
 
@@ -165,14 +167,24 @@ ${format(ms / libraryCount, 3, 12)} ms/compilation unit.""");
   ///
   /// If [wasHandled] is true, this error is added to [handledErrors],
   /// otherwise it is added to [unhandledErrors].
+  void addCompileTimeError(Message message, int charOffset, Uri fileUri,
+      {bool silent: false, bool wasHandled: false}) {
+    if (!silent) {
+      deprecated_printUnexpected(fileUri, charOffset, message.message);
+    }
+    (wasHandled ? handledErrors : unhandledErrors)
+        .add(message.withLocation(fileUri, charOffset));
+  }
+
   void deprecated_addCompileTimeError(
-      Uri fileUri, int charOffset, Object message,
+      Uri fileUri, int charOffset, String message,
       {bool silent: false, bool wasHandled: false}) {
     if (!silent) {
       deprecated_printUnexpected(fileUri, charOffset, message);
     }
-    (wasHandled ? handledErrors : unhandledErrors)
-        .add(new deprecated_InputError(fileUri, charOffset, message));
+    (wasHandled ? handledErrors : unhandledErrors).add(templateUnspecified
+        .withArguments(message)
+        .withLocation(fileUri, charOffset));
   }
 
   Builder getAbstractClassInstantiationError() {