improve fasta interpolation recovery

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

Index: pkg/front_end/lib/src/scanner/errors.dart
diff --git a/pkg/front_end/lib/src/scanner/errors.dart b/pkg/front_end/lib/src/scanner/errors.dart
index 17ef2134ef16863e42ae90e71c98fb74beb8e173..ca2a20972639926508bfc0aea952ad0044896006 100644
--- a/pkg/front_end/lib/src/scanner/errors.dart
+++ b/pkg/front_end/lib/src/scanner/errors.dart
@@ -94,7 +94,7 @@ void translateErrorToken(ErrorToken token, ReportError reportError) {
     case "UNTERMINATED_STRING_LITERAL":
       // TODO(paulberry,ahe): Fasta reports the error location as the entire
       // string; analyzer expects the end of the string.
-      charOffset = endOffset;
+      charOffset = endOffset - 1;
       return _makeError(ScannerErrorCode.UNTERMINATED_STRING_LITERAL, null);
 
     case "UNTERMINATED_MULTI_LINE_COMMENT":