improve fasta parser export declaration recovery

pkg/front_end/test/fasta/parser/token_stream_rewriter_test.dart

Index: pkg/front_end/test/fasta/parser/token_stream_rewriter_test.dart
diff --git a/pkg/front_end/test/fasta/parser/token_stream_rewriter_test.dart b/pkg/front_end/test/fasta/parser/token_stream_rewriter_test.dart
index e7d4a670ab5d9aa3454f04b7c02be96bea7c6976..70b8172461f415ee65647c35c75487c3a9d03c49 100644
--- a/pkg/front_end/test/fasta/parser/token_stream_rewriter_test.dart
+++ b/pkg/front_end/test/fasta/parser/token_stream_rewriter_test.dart
@@ -26,7 +26,7 @@ abstract class TokenStreamRewriterTest {
     var b = _makeToken(1, 'b');
     var eof = _link([a]);
     var rewriter = new TokenStreamRewriter(a);
-    rewriter.insertTokenBefore(b, eof);
+    expect(rewriter.insertTokenBefore(b, eof), same(b));
     expect(rewriter.firstToken, same(a));
     expect(a.next, same(b));
     expect(b.next, same(eof));
@@ -39,7 +39,7 @@ abstract class TokenStreamRewriterTest {
     var b = _makeToken(1, 'b');
     _link([b]);
     var rewriter = new TokenStreamRewriter(b);
-    rewriter.insertTokenBefore(a, b);
+    expect(rewriter.insertTokenBefore(a, b), same(a));
     expect(rewriter.firstToken, same(a));
     expect(a.next, same(b));
     expect(a.previous.next, same(a));