Use printUnexpected and add location information.

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

 // Copyright (c) 2016, 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 fasta.errors;
 
 import 'dart:async' show
     Future;
 
 import 'dart:convert' show
@@ skipping 47 matching lines @@
 ///
 /// An input error is any error that isn't an internal error. We use the term
 /// "input error" in favor of "user error". This way, if an input error isn't
 /// handled correctly, the user will never see a stack trace that says "user
 /// error".
 dynamic inputError(Uri uri, int charOffset, Object error) {
   throw new InputError(uri, charOffset, error);
 }
 
 String printUnexpected(Uri uri, int charOffset, String message) {
+  String formattedMessage = formatUnexpected(uri, charOffset, message);
   if (errorsAreFatal) {
+    print(formattedMessage);
     if (isVerbose) print(StackTrace.current);
     throw new InputError(uri, charOffset, message);
   }
-  message = formatUnexpected(uri, charOffset, message);
-  print(message);
-  return message;
+  print(formattedMessage);
+  return formattedMessage;
 }
 
 String formatUnexpected(Uri uri, int charOffset, String message) {
   return format(uri, charOffset, colorError("Error: $message"));
 }
 
 String colorError(String message) {
   // TODO(ahe): Colors need to be optional. Doesn't work well in Emacs or on
   // Windows.
   return red(message);
@@ skipping 94 matching lines @@
   return new Future.error(error, trace);
 }
 
 String safeToString(Object object) {
   try {
     return "$object";
   } catch (e) {
     return "Error when converting ${object.runtimeType} to string.";
   }
 }