Port parser and scanner fixes from rasta branch.

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

Index: pkg/front_end/lib/src/fasta/scanner.dart
diff --git a/pkg/front_end/lib/src/fasta/scanner.dart b/pkg/front_end/lib/src/fasta/scanner.dart
index 53d0122429ea4986a7db16a774708a9b33d74284..903fec27ef48023dff39ead13b9685bebf688db3 100644
--- a/pkg/front_end/lib/src/fasta/scanner.dart
+++ b/pkg/front_end/lib/src/fasta/scanner.dart
@@ -4,6 +4,9 @@
 
 library fasta.scanner;
 
+import 'dart:convert' show
+    UNICODE_REPLACEMENT_CHARACTER_RUNE;
+
 import 'scanner/token.dart' show
     Token;
 
@@ -15,7 +18,6 @@ import 'scanner/recover.dart' show
 
 export 'scanner/token.dart' show
     BeginGroupToken,
-    ErrorToken,
     KeywordToken,
     StringToken,
     SymbolToken,
@@ -26,6 +28,10 @@ export 'scanner/token.dart' show
     isUnaryOperator,
     isUserDefinableOperator;
 
+export 'scanner/error_token.dart' show
+    ErrorToken,
+    buildUnexpectedCharacterToken;
+
 export 'scanner/token_constants.dart' show
     EOF_TOKEN;
 
@@ -38,6 +44,8 @@ export 'scanner/string_scanner.dart' show
 export 'scanner/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 {