Implement line and column numbers.

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

Index: pkg/front_end/lib/src/fasta/errors.dart
diff --git a/pkg/front_end/lib/src/fasta/errors.dart b/pkg/front_end/lib/src/fasta/errors.dart
index 077f1609ba19867c24fb8d1581b9735e1b732830..fb5d27105f0b2de44ad38d0651309deedde9a9c1 100644
--- a/pkg/front_end/lib/src/fasta/errors.dart
+++ b/pkg/front_end/lib/src/fasta/errors.dart
@@ -20,8 +20,7 @@ import 'dart:io' show
 import 'colors.dart' show
     red;
 
-import 'util/relativize.dart' show
-    relativizeUri;
+import 'messages.dart' as messages;
 
 const String defaultServerAddress = "http://127.0.0.1:59410/";
 
@@ -41,8 +40,13 @@ Uri firstSourceUri;
 /// error: " and a short description that may help a developer debug the issue.
 /// This method should be called instead of using `throw`, as this allows us to
 /// ensure that there are no throws anywhere in the codebase.
-dynamic internalError(Object error) {
-  throw error;
+dynamic internalError(Object error, [Uri uri, int charOffset = -1]) {
+  if (uri == null && charOffset == -1) {
+    throw error;
+  } else {
+    throw messages.format(
+        uri, charOffset, "Internal error: ${safeToString(error)}");
+  }
 }
 
 /// Used to report an error in input.
@@ -58,6 +62,12 @@ dynamic inputError(Uri uri, int charOffset, Object error) {
   throw new InputError(uri, charOffset, error);
 }
 
+String colorError(String message) {
+  // TODO(ahe): Colors need to be optional. Doesn't work well in Emacs or on
+  // Windows.
+  return red(message);
+}
+
 class InputError {
   final Uri uri;
 
@@ -71,15 +81,8 @@ class InputError {
   toString() => "InputError: $error";
 
   String format() {
-    // TODO(ahe): Colors need to be optional. Doesn't work well in Emacs or on
-    // Windows.
-    String message = red("Error: ${safeToString(error)}");
-    if (uri != null) {
-      String position = charOffset == -1 ? "" : "$charOffset:";
-      return "${relativizeUri(uri)}:$position $message";
-    } else {
-      return message;
-    }
+    return messages.format(
+        uri, charOffset, colorError("Error: ${safeToString(error)}"));
   }
 }