Port parser and scanner fixes from rasta branch.

pkg/dart_scanner/lib/dart_scanner.dart

Index: pkg/dart_scanner/lib/dart_scanner.dart
diff --git a/pkg/dart_scanner/lib/dart_scanner.dart b/pkg/dart_scanner/lib/dart_scanner.dart
index f9e5374deacc6226d0fe173486627e4ec169007e..e2bc3b4748b6bc7ab1383786e74a8d8ecf6e678f 100644
--- a/pkg/dart_scanner/lib/dart_scanner.dart
+++ b/pkg/dart_scanner/lib/dart_scanner.dart
@@ -4,6 +4,9 @@
 
 library dart_scanner;
 
+import 'dart:convert' show
+    UNICODE_REPLACEMENT_CHARACTER_RUNE;
+
 import 'src/token.dart' show
     Token;
 
@@ -15,7 +18,6 @@ import 'src/recover.dart' show
 
 export 'src/token.dart' show
     BeginGroupToken,
-    ErrorToken,
     KeywordToken,
     StringToken,
     SymbolToken,
@@ -26,6 +28,10 @@ export 'src/token.dart' show
     isUnaryOperator,
     isUserDefinableOperator;
 
+export 'src/error_token.dart' show
+    ErrorToken,
+    buildUnexpectedCharacterToken;
+
 export 'src/token_constants.dart' show
     EOF_TOKEN;
 
@@ -38,6 +44,8 @@ export 'src/string_scanner.dart' show
 export 'src/keyword.dart' show
     Keyword;
 
+const int unicodeReplacementCharacter = UNICODE_REPLACEMENT_CHARACTER_RUNE;
+
 typedef Token Recover(List<int> bytes, Token tokens, List<int> lineStarts);
 
 abstract class Scanner {