Correctly recover from incorrect imports, etc.

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

 // Copyright (c) 2012, 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.parser.parser;
 
 import '../scanner.dart' show ErrorToken;
 
 import '../scanner/recover.dart' show closeBraceFor, skipToEof;
 
@@ skipping 1436 matching lines @@
     mayParseFunctionExpressions = old;
     listener.endInitializers(count, begin, token);
     return token;
   }
 
   Token parseLiteralStringOrRecoverExpression(Token token) {
     if (identical(token.kind, STRING_TOKEN)) {
       return parseLiteralString(token);
     } else {
       reportRecoverableError(token, ErrorKind.ExpectedString);
-      return parseExpression(token);
+      return parseRecoverExpression(token);
     }
   }
 
   Token expectSemicolon(Token token) {
     return expect(';', token);
   }
 
   bool isModifier(Token token) {
     final String value = token.stringValue;
     return (identical('final', value)) ||
@@ skipping 948 matching lines @@
         BeginGroupToken begin = token;
         token = (begin.endGroup != null) ? begin.endGroup : token;
       } else if (token is ErrorToken) {
         reportErrorToken(token, false);
       }
       token = token.next;
     }
     return token;
   }
 
+  Token parseRecoverExpression(Token token) => parseExpression(token);
+
   int expressionDepth = 0;
   Token parseExpression(Token token) {
     if (expressionDepth++ > 500) {
       // This happens in degenerate programs, for example, with a lot of nested
       // list literals. This is provoked by, for examaple, the language test
       // deep_nesting1_negative_test.
       return reportUnrecoverableError(token, ErrorKind.StackOverflow);
     }
     listener.beginExpression(token);
     Token result = optional('throw', token)
@@ skipping 1121 matching lines @@
         break;
     }
     if (isRecoverable) {
       listener.handleRecoverableError(token, kind, arguments);
       return null;
     } else {
       return listener.handleUnrecoverableError(token, kind, arguments);
     }
   }
 }