improve parser recovery for import directives

pkg/analyzer/lib/src/generated/parser.dart

Index: pkg/analyzer/lib/src/generated/parser.dart
diff --git a/pkg/analyzer/lib/src/generated/parser.dart b/pkg/analyzer/lib/src/generated/parser.dart
index 50db79161cab990df939a00c2bdc7c6078ea3810..0d2cbc08af064eb694c273ed3920973d8a50b3e4 100644
--- a/pkg/analyzer/lib/src/generated/parser.dart
+++ b/pkg/analyzer/lib/src/generated/parser.dart
@@ -5952,7 +5952,7 @@ class Parser {
    * associated with the directive. Return the import directive that was parsed.
    *
    *     importDirective ::=
-   *         metadata 'import' stringLiteral ('as' identifier)? combinator*';'
+   *         metadata 'import' stringLiteral (deferred)? ('as' identifier)? combinator*';'
    */
   ImportDirective _parseImportDirective(CommentAndMetadata commentAndMetadata) {
     Token importKeyword = _expectKeyword(Keyword.IMPORT);
@@ -5969,6 +5969,13 @@ class Parser {
     } else if (deferredToken != null) {
       _reportErrorForCurrentToken(
           ParserErrorCode.MISSING_PREFIX_IN_DEFERRED_IMPORT);
+    } else if (!_matches(TokenType.SEMICOLON) &&
+        _tokenMatchesKeyword(_peek(), Keyword.AS)) {
+      _reportErrorForCurrentToken(
+          ParserErrorCode.UNEXPECTED_TOKEN, [_currentToken]);
+      _advance();
+      asToken = getAndAdvance();
+      prefix = parseSimpleIdentifier();
     }
     List<Combinator> combinators = _parseCombinators();
     Token semicolon = _expectSemicolon();