fasta.BeginGroupToken implement analyzer.BeginToken

pkg/analyzer/lib/src/fasta/token_utils.dart

Index: pkg/analyzer/lib/src/fasta/token_utils.dart
diff --git a/pkg/analyzer/lib/src/fasta/token_utils.dart b/pkg/analyzer/lib/src/fasta/token_utils.dart
index 759ccb01a8a6ca35ad0003cd2ee9a2cf374da1f9..39b4c63c1bb17bb064da923e45193af20a65e5e6 100644
--- a/pkg/analyzer/lib/src/fasta/token_utils.dart
+++ b/pkg/analyzer/lib/src/fasta/token_utils.dart
@@ -238,6 +238,7 @@ analyzer.CommentToken toAnalyzerCommentToken(Token token) {
 /// information.
 Token fromAnalyzerTokenStream(analyzer.Token analyzerToken) {
   Token tokenHead = new SymbolToken(EOF_INFO, -1);
+  tokenHead.previous = tokenHead;
   Token tokenTail = tokenHead;
 
   // Both fasta and analyzer have links from a "BeginToken" to its matching
@@ -316,6 +317,7 @@ Token fromAnalyzerTokenStream(analyzer.Token analyzerToken) {
       tokenTail.next.previousToken = tokenTail;
       tokenTail.next.precedingCommentTokens =
           translateComments(analyzerToken.precedingComments);
+      tokenTail.next.next = tokenTail.next;
       return tokenHead.next;
     }
     analyzerToken = translateAndAppend(analyzerToken);