Improve error recovery in parser.

dart/frog/leg/scanner/listener.dart

Index: dart/frog/leg/scanner/listener.dart
diff --git a/dart/frog/leg/scanner/listener.dart b/dart/frog/leg/scanner/listener.dart
index f6a320237aef78f6ff375bd791009cc3383d0398..1c4559c111fc65c3fa2cea8836912ec217095871 100644
--- a/dart/frog/leg/scanner/listener.dart
+++ b/dart/frog/leg/scanner/listener.dart
@@ -387,22 +387,34 @@ class Listener {
 
   Token expected(String string, Token token) {
     error("Expected '$string', but got '$token'", token);
+    return skipToEof(token);
   }
 
   void expectedIdentifier(Token token) {
     error("Expected identifier, but got '$token'", token);
+    return skipToEof(token);
   }
 
   Token expectedType(Token token) {
     error("Expected a type, but got '$token'", token);
+    return skipToEof(token);
   }
 
   Token expectedBlock(Token token) {
     error("Expected a block, but got '$token'", token);
+    return skipToEof(token);
   }
 
   Token unexpected(Token token) {
     error("Unexpected token '$token'", token);
+    return skipToEof(token);
+  }
+
+  skipToEof(Token token) {
+    while (token.info !== EOF_INFO) {
+      token = token.next;
+    }
+    return token;
   }
 
   void recoverableError(String message, [Token token, Node node]) {
@@ -566,22 +578,27 @@ class ElementListener extends Listener {
 
   Token expected(String string, Token token) {
     canceler.cancel("Expected '$string', but got '$token'", token: token);
+    return skipToEof(token);
   }
 
   void expectedIdentifier(Token token) {
     canceler.cancel("Expected identifier, but got '$token'", token: token);
+    return skipToEof(token);
   }
 
   Token expectedType(Token token) {
     canceler.cancel("Expected a type, but got '$token'", token: token);
+    return skipToEof(token);
   }
 
   Token expectedBlock(Token token) {
     canceler.cancel("Expected a block, but got '$token'", token: token);
+    return skipToEof(token);
   }
 
   Token unexpected(Token token) {
     canceler.cancel("Unexpected token '$token'", token: token);
+    return skipToEof(token);
   }
 
   void recoverableError(String message, [Token token, Node node]) {