more fixes for fasta analyzer integration

pkg/front_end/lib/src/fasta/scanner/token.dart

Index: pkg/front_end/lib/src/fasta/scanner/token.dart
diff --git a/pkg/front_end/lib/src/fasta/scanner/token.dart b/pkg/front_end/lib/src/fasta/scanner/token.dart
index afbe541f58289c7073d86a7812bb6d00f9ea7df1..b7a9b5d23905f462859291e1a2deaf11cb77bf39 100644
--- a/pkg/front_end/lib/src/fasta/scanner/token.dart
+++ b/pkg/front_end/lib/src/fasta/scanner/token.dart
@@ -118,7 +118,7 @@ class StringToken extends analyzer.TokenWithComment
 
   @override
   Token copy() => new StringToken._(
-      type, valueOrLazySubstring, charOffset, precedingComments);
+      type, valueOrLazySubstring, charOffset, copyComments(precedingComments));
 
   @override
   String value() => lexeme;
@@ -138,7 +138,7 @@ class SyntheticStringToken extends StringToken
 
   @override
   Token copy() => new SyntheticStringToken(
-      type, valueOrLazySubstring, offset, precedingComments);
+      type, valueOrLazySubstring, offset, copyComments(precedingComments));
 }
 
 class CommentToken extends StringToken implements analyzer.CommentToken {